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Cannabidiol Adverse Effects and Toxicity 1 Lambert Center for the Study of Medicinal Cannabis and Hemp, Institute of Emerging Health Professions, Thomas Jefferson University, Philadelphia, PA, CBD oil is considered to have a very high safety profile, but like any substance with the ability to change brain chemistry, its use can have some side effects. Curious about how CBD affects the body? CBD has many promising uses. See how it may be able to help with your condition.

Cannabidiol Adverse Effects and Toxicity

1 Lambert Center for the Study of Medicinal Cannabis and Hemp, Institute of Emerging Health Professions, Thomas Jefferson University, Philadelphia, PA, USA;
2 National Centre on Addiction and Doping, Istituto Superiore di Sanità, Rome, Italy;
3 Unit of Forensic Toxicology (UoFT), Department of Anatomical, Histological, Forensic and Orthopedic Sciences, Sapienza University of Rome, Rome, Italy;
4 Section of Legal Medicine, Università Politecnica delle Marche, Ancona, Italy

* Address correspondence to this author at the Section of Legal Medicine, Università Politecnica delle Marche, Ancona, Italy; Tel: 3932244667; E-mail: [email protected]



Currently, there is a great interest in the potential medical use of cannabidiol (CBD), a non-intoxicating cannabinoid. Productive pharmacological research on CBD occurred in the 1970s and intensified recently with many discoveries about the endocannabinoid system. Multiple preclinical and clinical studies led to FDA-approval of Epidio-lex®, a purified CBD medicine formulated for oral administration for the treatment of infantile refractory epileptic

syndromes, by the US Food and Drug Administration in 2018. The World Health Organization considers rescheduling can-nabis and cannabinoids. CBD use around the world is expanding for diseases that lack scientific evidence of the drug’s effi-cacy. Preclinical and clinical studies also report adverse effects (AEs) and toxicity following CBD intake.


Relevant studies reporting CBD’s AEs or toxicity were identified from PubMed, Cochrane Central, and EMBASE through January 2019. Studies defining CBD’s beneficial effects were included to provide balance in estimating risk/benefit.


CBD is not risk-free. In animals, CBD AEs included developmental toxicity, embryo-fetal mortality, central nerv-ous system inhibition and neurotoxicity, hepatocellular injuries, spermatogenesis reduction, organ weight alterations, male reproductive system alterations, and hypotension, although at doses higher than recommended for human pharmacotherapies. Human CBD studies for epilepsy and psychiatric disorders reported CBD-induced drug-drug interactions, hepatic abnormal-ities, diarrhea, fatigue, vomiting, and somnolence.


CBD has proven therapeutic efficacy for serious conditions such as Dravet and

Lennox-Gastaut syndromes and is likely to be recommended off label by physicians for other conditions. However, AEs and potential drug-drug interactions must be taken into consideration by clinicians prior to recommending off-label CBD.

Keywords: Cannabidiol, adverse effects, toxicity, animal studies, in vitro studies, in vivo studies, studies in humans


1.1. Cannabinoid Pharmacology

Δ9-tetrahydrocannabinol (THC) was shown to be the primary psychoactive compound in cannabis (marijuana) in 1964 by Gaoni and Mechoulam [1]. There were few advances in cannabinoid pharmacology until 1988, when Devane et al. identified the first CB1 cannabinoid receptor [2], quickly followed by the discovery of the CB2 peripheral receptor by Munro et al. in 1990 [3]. The CB1 and CB2

cannabinoid receptors were cloned by Matsuda et al. in 1992 [4] and Munro et al. in 1993 [3], respectively. However, the endogenous cannabinoid system may include additional cannabinoid G protein-coupled receptors (GPCR) GPR55, GPR18, and GPR119, transient receptor potential cation channels (TRP) TRPV, TRPA, TRPM, and TRPC and nuclear peroxisome proliferator-activated receptors (PPAR) [5]. Anandamide was the first identified endogenous cannabinoid ligand [6], but there are many other endocannabinoids including 2-arachidonylglycerol, N-palmitoyl ethanolamide, and N-oleoyl ethanolamide.

Cannabidiol (CBD or 2-[(6R)-6-isopropenyl-3-methyl-2-cyclohexen-1-yl]-5-pentyl-1,3-benzene-diol) was identified in an extract of Minnesota wild hemp by Adams et al. at the University of Illinois in 1940 [7], but its structure was not fully elucidated until 1963 [8]. To date, CBD’s mechanisms of action are not fully elucidated [9]. CBD modulates central nervous system (CNS) receptors such as CB1, CB2, serotonin 1A receptor (5-HT1A), TRPV1, and PPARγ, although it binds poorly to the THC-binding site on CB1 and CB2 cannabinoid receptors [10]. CBD may antagonize CB1 receptor function by negative allosteric modulation of the orthosteric receptor site [11-14]. CBD may be an inverse agonist at the CB2 receptor, partially explaining its anti-inflammatory properties [15], which also are supported by CBD PPARɤ activation [16]. High CBD doses activate TRPV1 receptors promoting anxiolytic effects [17]. CBD also increases serotoninergic and glutamatergic transmission through a positive allosteric modulation of 5-HT1A serotonin receptors [10]. 5-HT1A receptor activation is also involved in CBD neuroprotection in in vitro adult and rat newborn models of the acute hypoxic-ischemic brain [18].

CBD is metabolized in the liver and the intestine by cytochrome P450 (CYP) CYP2C19 and CYP3A4, and 5′-diphosphoglucuronosyltransferase (UGT) UGT1A7, UGT1A9, and UGT2B7 isoforms, mainly producing hydroxylated and carboxylated metabolites [19]. CBD inhibited barbiturate metabolism, increasing barbiturate-induced sleep duration in mice, and also phenazone hepatic metabolism [20] due to the inhibition of CYP3A and CYP2C microsomal enzymes [21]. Other research suggested that CBD also induced hepatic CYP3A, CYP2B, and CYP2C [22]. Later, CBD was shown to inhibit THC metabolic hydroxylation in humans. The pharmacokinetic interaction between THC and CBD may explain why CBD administration prior to THC potentiates THC effects [23].

The complexity of CBD pharmacology offers tremendous therapeutic potential but also the potential for AEs and drug-drug interactions.

1.2. Potential Therapeutic Effects of CBD

In 2017, the National Academies of Science, Engineering and Medicine evaluated all the published literature through August, 2016 on the potential therapeutic uses of cannabinoids [24]. They determined if there was conclusive evidence, substantial evidence, moderate evidence, limited evidence, or insufficient evidence for cannabinoids being an effective or ineffective therapy to treat chronic pain, cancer, chemotherapy-induced nausea/vomiting, appetite and weight loss, irritable bowel syndrome, epilepsy, spasticity of multiple sclerosis, Tourette syndrome, amyotrophic lateral sclerosis, Huntington’s disease, Parkinson’s disease, dystonia, Alzheimer’s disease/dementia, glaucoma, traumatic brain injury/spinal cord injury, addiction, anxiety, depression, sleep disorders, posttraumatic stress disorder, and schizophrenia. In addition, they reviewed the knowledge base using the same evidence categories for the health effects of cannabinoids and cancer, cardiometabolic risk, acute myocardial infarction, stroke, metabolic dysregulation, metabolic syndrome, diabetes, respiratory disease, immunity, injury and death, prenatal, perinatal, and postnatal exposure to cannabis, psychosocial, mental health, and problem cannabis use.

This review is not focused on therapeutic indications but rather on potential AEs, toxicities and drug-drug interactions that may accompany CBD therapeutics and that must be considered prior to off-label use of CBD for pathophysiology that has not yet been shown to respond effectively to CBD. However, to enable the reader to independently evaluate CBD’s AEs and toxicity, we briefly highlight some current research supporting CBD therapeutics.

1.3. Anti-epileptic

As early as 1980, the potential therapeutic effect of 200-300 mg/day CBD in patients with uncontrolled epilepsy was evaluated [25]. Patients tolerated CBD well, with no signs of toxicity or serious side effects detected. Seven of 8 subjects receiving CBD had fewer convulsive episodes, with 3 only partially improved. A 2018 meta-analysis concluded that CBD in conjunction with other anti-epileptic drugs decreased seizure frequency in patients with Dravet’s and Lennox-Gastaut syndromes or who experienced intractable seizures, although AEs occurred more frequently than placebo [26]. The US Food and Drug Administration (FDA) approved Epidiolex ® for the treatment of refractory epilepsy in 2018 [19, 27].

1.4. Anxiolytic

Multiple studies evaluated the potential therapeutic effect of CBD on anxiety, psychotic symptoms, and depression in humans since the 1980s, mostly showing mild AEs [28-35]. CBD effectively treated anxiety by activating limbic and paralimbic regions of the brain [30].

Interestingly, a single acute administration of a low 3 mg/kg CBD dose in mice had an anxiolytic effect, while repeated administration of a 3 or 10 mg/kg dose exerted antidepressant effects by cell proliferation and neurogenesis [36]. Conversely, CBD anxiolytic effects were not observed at higher 10 and 30 mg/kg CBD doses or after 15 days of 30 mg/kg/day dosing. The authors suggest that there is an inverted U-shaped dose-response curve for CBD’s effects on anxiety.

1.5. Antipsychotic Properties

CBD is extensively studied for its antipsychotic effects on schizophrenia [35, 37]. Leweke et al. noted that CBD moderately inhibits degradation of the endocannabinoid anandamide [38]. They performed a double-blind, randomized clinical trial of CBD vs. amisulpride, a potent antipsychotic, in acute schizophrenia. Both treatments were safe and significant clinical improvement was achieved, but CBD had a better side effect profile. CBD treatment significantly increased serum anandamide concentrations.

The safety and effectiveness of 1000 mg/day CBD in patients with schizophrenia were assessed [35]. These patients (n=43) with schizophrenia received 1000 mg/day CBD in addition to their existing antipsychotic medications. After 6 weeks of treatment, the CBD group had lower levels of positive psychotic symptoms (positive and negative syndrome scale (PANSS): treatment difference=21.4, 95% CI=22.5,20.2). CBD was well tolerated, and AEs were similar between the CBD and placebo groups.

Six-hundred mg oral CBD was evaluated for its effects on persecutory ideation and anxiety in a high paranoid trait group (n=32) 130 min before entering a virtual-reality scenario [39]. CBD had no impact on anxiety (Beck’s anxiety inventory), or cortisol concentration, systolic blood pressure, and heart rate. In fact, in this study, a strong trend towards increased anxiety was documented and CBD had no effect on persecutory ideation.

1.6. CBD Neuroprotection

CBD’s anti-inflammatory and antioxidant properties may offer a new pharmacological approach for neuroprotection and a reduction in hippocampal volume loss [23, 40, 41]. CBD protects against hippocampal pathology following chronic frequent THC use [42]. This CBD restorative effect on hippocampal substructures suggests a therapeutic potential for other pathologies such as schizophrenia, Alzheimer’s disease, and major depressive disorder [40]. Indeed, in human studies for schizophrenia [35, 38] and Parkinson’s disease [43], and in animal studies for symptoms of Alzheimer’s disease [44], CBD was shown to be an effective treatment.

1.7. Spasticity

Many of the double-blinded, placebo-controlled studies for the effects of cannabinoids on spasticity used whole plant cannabis extracts or Sativex ® that is a 1:1 THC:CBD extract containing 2.5 to 120 mg THC and CBD/day. Visual Analogue Scale (VAS) scores for each patient’s most troublesome symptom were significantly reduced [45].

1.8. Chronic Pain

In adults with chronic pain, patients treated with cannabis or cannabinoids are more likely to experience a clinically significant reduction in pain symptoms [24]. A recent review of specific cannabinoids and cannabinoid extracts on multiple pain types investigates both the preclinical and clinical data supporting cannabinoid pharmacotherapy for pain [46].

1.9. Cancer

There is tremendous interest in CBD as an anticancer agent. Aviello et al. showed that CBD had multiple chemopreventive effects in murine colorectal carcinoma cell lines by protecting DNA from oxidative damage, increasing endocannabinoid concentrations and reducing cell proliferation in a CB1-, TRPV1- and PPARγ-antagonists sensitive manner [47]. De Petrocellis et al. found that 1-10 µM CBD significantly inhibited human prostate carcinoma cell viability, inducing apoptosis and elevation of reactive oxygen species (ROS) [48]. Exciting new developments for enhancing CBD effects in inducing cell death and enhancing radiosensitivity of glioblastoma (GBM) cells were recently published [49]. GBM cells treated with CBD, γ-irradiation, and KU60019, an ATM kinase inhibitor, increased apoptosis and with strongly upregulated arrested cells, blockade of cell proliferation, and production of pro-inflammatory cytokines, improving CBD effectiveness.

1.10. Addiction Disorders

Recently, Solowij et al. described a 10-week study of daily 200 mg CBD in cannabis dependence to improve psychological symptoms and cognition [41]. CBD was well tolerated with no serious AE, promising therapeutic effects for improving psychological symptoms and cognition in regular cannabis users, and suggested that CBD may be a useful adjunct treatment for cannabis dependence. CBD improved subicular and CA1 subfields volumes in the brains of chronic cannabis users, suggesting a protective role of CBD against brain structural harms conferred by chronic cannabis use [40]. Moreover, CBD was shown to have low abuse liability [50, 51] and to be effective in decreasing cannabis addiction [52, 53].

1.11. The Current Context

In June 2018, the US FDA approved the marketing of Epidiolex ® , a CBD-rich whole cannabis plant extract, for the treatment of seizures in patients over age two suffering from Lennox-Gastaut and Dravet syndromes, two drug-resistant forms of epilepsy with a higher early mortality rate [27]. The studies that led to FDA approval of Epidiolex ® for the treatment of severe forms of epilepsy, used CBD as an adjunct to clobazam, valproate, levetiracetam, and topiramate, resulting in seizures reduction with few AEs, compared to other drugs.

In January 2019, the World Health Organization (WHO) changed position after 60 years and proposed rescheduling of cannabis and cannabinoids for therapeutic purposes [54, 55]. Three months after FDA Epidiolex ® approval, the U.S. Drug Enforcement Administration (DEA) removed Epidiolex ® from the most restricted Schedule 1 (no approved medical use and high abuse liability) to Schedule V with low abuse potential [56].

In the wake of growing medical and public interest in medical cannabis and cannabinoids, we aimed to evaluate current knowledge of CBD’s AEs and toxicities by the relevant scientific literature from preclinical and clinical studies. Clinicians should be aware of CBD AEs and potential drug-drug interactions prior to recommending off-label CBD.


A literature search, from inception to January 2019, was performed on PubMed, EMBASE, and CENTRAL (Cochrane Central Register of Controlled Trials) using the keywords cannabidiol, Epidiolex, adverse or side effects, adverse reactions or events, safety, complications, toxicity, and toxicology. Relevant articles were selected by the following criteria: articles acknowledging CBD AEs or toxicity, including studies focusing on the beneficial effects of the drug, and published in English. Several studies defining CBD’s beneficial effects were included to provide balance and aid the readers’ ability to weigh risk/benefit.

Further research manuscripts were retrieved through the reference lists of selected articles, and reports were found on international agencies or institutional websites including US FDA, WHO, US DEA, and US National Academies of Sciences, Engineering, and Medicine. All articles were screened independently by three co-authors to determine their relevance and included if selected by at least two co-authors.


CBD clearly has great potential as a new pharmacotherapy based on novel mechanisms of action for currently unmet clinical needs. However, CBD, like almost all medications, also produces AEs and toxicity. Two previous reviews focused on the therapeutic effects but also included AEs. In 2011, Bergamaschi et al. reviewed CBD AEs in animals and humans, concluding that CBD is generally safe, but further research is needed to investigate in-depth the observed in vitro and in vivo AEs [57]. In 2017, Iffland and Grotenhermen confirmed CBD’s safety profile, especially compared to other antiepileptics and antipsychotics [58]. These authors suggested that research should pursue AEs of chronic administration, hormonal effects, enzyme inhibition or induction, genotoxicity, drug transporters, and interactions with other drugs.

Currently, CBD is the focus of mass marketing campaigns and the subject of anecdotal reports claiming that CBD provides the answer for multiple illnesses from chronic pain to depression. Despite its Schedule I status in the US by the DEA, and lack of control by the FDA, CBD products are sold across the US and the internet. No medication should be prescribed or recommended until it is proven safe and effective for each indication under consideration. In addition, it is important to reflect whether the medication is safe for each individual based on his or her health, age, genetics, chronic illnesses, and other medications (due to the problem of drug-drug interactions). Now that Epidiolex ® is FDA-approved, off-label prescriptions will increase. The goal of this review is to inform clinicians, pharmacists, nurses, patients, public health authorities, and policymakers about CBD’s AEs, toxicities, and drug-drug interactions that should be evaluated prior to prescribing CBD.

Table ​ 1 1 lists AEs identified in preclinical research, and Table ​ 2 2 , AEs identified in clinical research. Both Tables ​ 1 1 and 2 list AEs in chronological order.

Table 1

Species CBD Dose Route Reported Adverse Effects (AEs) Refs.
Acute AEs
Rats 0.6, 0.8, or 1.2 mg/kg Inhaled Organ weight elevation; Seminiferous tubule degeneration, interference in sperm maturation Rosenkrantz and Hayden, 1979 [100]
Rhesus monkeys 150, 200, 225, 250, or 300 mg/kg/day (9 days) Intravenous Tremors, central nervous system inhibition, convulsions, bradycardia, hypopnea, cardiac failure at higher doses; Liver weight increase and testicular weights decrease, inhibition of spermatogenesis Rosenkrantz and Hayden, 1981 [61]
Sea urchin eggs and sperms 0.1, 0.5, 1.0, or 10 µM Incubation in CBD-enriched sea water Dose-dependent decreased fertility of eggs & sperms & fertilization inhibition Schuel et al., 1987 [101]
Rats 10 mg/kg Intraperitoneal Decrease of testosterone metabolism; Decrease of CYP aniline hydroxylation and p-nitroanisole demethylation, alteration of CYP contents Narimatsu et al., 1990 [86]
Sea urchin sperms 0.1–100 µM Incubation in CBD-enriched sea water Dose and time-dependent acrosome reaction inhibition, motility not reduced Schuel et al., 1991 [102]
Piglets 10, 25, or 50 mg/kg Intravenous Hypotension, cardiac arrest Garberg et al., 2017 [63]
Rats 10 mg/kg + 10 mg/kg THC Subcutaneous THC metabolism inhibition with higher THC concentrations & lower CBD concentrations in serum and brain; Hypolocomotion: THC metabolism inhibition shows little to no impact on THC-induced behavior Hložek et al., 2017 [96]
Rats 10 mg/kg + 10 mg/kg THC Oral THC metabolism inhibition with higher THC concentrations & lower CBD concentrations in serum and brain; Almost total immobility (10 mg/kg CBD alone caused mild hyperlocomotion): THC metabolism inhibition shows little to no impact on THC-induced behavior Hložek et al., 2017 [96]
Rats 10 mg + 10 mg THC (5 min vaporization) Inhaled No THC metabolism inhibition Hložek et al., 2017 [96]
Chronic AEs
Rhesus monkeys 30, 100, or 300 mg/kg/day (90 days) Oral Liver, heart, kidney, and thyroid weight increase; Decrease in testicular size, spermatogenesis inhibition Rosenkrantz and Hayden, 1981 [61]
Rats 10 mg/kg (14 days) Intraperitoneal Anxiogenic-like effect, decreased brain-derived neurotrophic factor (BDNF) expression & related signaling proteins in the hippocampus and frontal cortex; Protein expression decrease in animals with enhanced protein expression following chronic antidepressant/anxiolytic drug treatment ElBatsh et al., 2012 [79]
Mice 30 mg/kg (15 days) Intraperitoneal Decreased cell proliferation and neurogenesis in the hippocampus and in subgranular zone Schiavon et al., 2016 [36]
Rats (pregnant) 75, 150, or 250 mg/kg/day (during organogenesis) Oral Developmental toxicity, increased embryofetal mortality Center for Drug Evaluation and Research, 2018 [103]
Rats (pregnant) 75, 150, or 250 mg/kg/day (during pregnancy and lactation) Oral Decreased growth, delayed sexual maturation, neurobehavioral changes, alterations of male reproductive organ development & fertility in offspring Center for Drug Evaluation and Research, 2018 [103]
Rabbits (pregnant) 50, 80, or 125 mg/kg/day (during organogenesis) Oral Decreased fetal body weight, increased fetal
structural variations
Center for Drug Evaluation and
Research, 2018 [103]
Mice 15 or 30 mg/kg (34 days) Oral Decreased circulating testosterone, increased frequency of mitotic stages I-VI, decrease in spermiation stages VII-VIII & meiotic stage XII, decrease in number of Sertoli cells at meiotic stage (XII), decrease in number of spermatozoa in the epididymis tail, head abnormalities in sperm, cytoplasmic droplets in the flagella medial region Carvalho et al., 2018 [104]
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Table 2

Oral CBD Dose Simultaneous Drug
Reported Adverse Effects (AEs) Refs.
Neurological studies
Parental report: online survey Age 2-16; 18 patients with Dravet syndrome, Lennox-Gastaut syndrome, Doose syndrome, or idiopathic epilepsy 0.5–28.6 mg/kg/day (2 weeks–12 months) Not reported Moderate (defined as: sufficiently discomforting so as to limit or interfere with daily activities and may require interventional treatment): drowsiness (37%), fatigue (16%) Porter and Jacobson, 2013 [68]
Parental report: online survey Age 3-10; 117 patients with Dravet syndrome, Lennox-Gastaut syndrome, or infantile spasms Median of 4.3 mg/kg/day (6.8 months) Clobazam, other not-specified antiepileptics AEs in 59% patients; Moderate: increased appetite, weight gain, drowsiness Hussain et al., 2015 [67]
Open-label study, expanded-access trial in 11 independent epilepsy centers Age 1-30; Patients with treatment-resistant epilepsy; 162 patients in safety analysis group (33 with Dravet syndrome, 31 with Lennox-Gastaut syndrome) 2–5 mg/kg/day increased until intolerance or to a maximum of 25–50 mg/kg/day (12 weeks) Clobazam, valproate AEs in 79% safety group patients (128/162); Moderate: somnolence, fatigue, lethargy, sedation, decreased or changes in appetite, diarrhea, transaminases increase, changes of antiepileptics serum concentration; Severe: status epilepticus, convulsions, diarrhea, weight loss, thrombocytopenia, hyperammonaemia, hepatotoxicity Devinsky et al., 2016 [70]
Retrospective study with no control group Age 1-18; 74 patients with treatment-resistant epilepsy 1–20 mg/kg/day;
81% patients (60/74) with < 10 mg/kg, 19% (14/74) with >10 mg/kg (> 3 months, average 6 months)
Not reported AEs reported in 47% patients (34/74); Moderate: seizure aggravation (5 patients stopped CBD treatment due to seizure aggravation), somnolence, fatigue, gastrointestinal disturbances, irritability Tzadok et al., 2016 [69]
Double-blind, randomized, placebo-controlled trial Age 2-18; 120 patients with Dravet syndrome 20 mg/kg/day (14 weeks) Median of 3 antiepileptics (e.g., clobazam, valproate) AEs in 93% patients; Moderate: diarrhea, loss of appetite, lethargy, fatigue, pyrexia, convulsion, elevated aminotransferase levels, somnolence; Severe (10 patients): elevated levels of liver aminotransferase enzymes (n=3), status epilepticus (n=3) Devinsky et al., 2017 [71]
Double-blind, randomized, placebo-controlled trial Age 4-10; 34 patients with Dravet syndrome 5, 10, or 20 mg/kg/day (4-week baseline, 3-week treatment, 10-day taper, and 4-week follow-up) Clobazam, valproate, levetiracetam, topiramate, stiripentol Treatment-emergent AEs (TEAEs) reported in 80% patients with 5 mg/kg (8/10), 63% patients with 10 mg/kg (6/8), 78% patients with 20 mg/kg (7/9), 86% patients with placebo (6/7); Moderate: pyrexia, sedation, somnolence, appetite loss, vomiting, ataxia, abnormal behavior, rash; Severe: pyrexia, maculopapular rash, elevated transaminases Devinsky et al., 2018 [74]
Double-blind, randomized, placebo-controlled trial Age 2-55; 225 patients with Lennox-Gastaut syndrome 10 or 20/mg/kg/day (28 days) Not-specified antiepileptics AEs in 84% patients with 10 mg/kg (56/67), in 94% patients with 20 mg/kg (77/82); Moderate: somnolence, decreased appetite, diarrhea, upper respiratory tract infection, pyrexia, vomiting; Severe: elevated aspartate aminotransferase (AST) concentration, elevated alanine aminotransferase (ALT) concentration, elevated γ-glutamyltransferase concentration, somnolence, increased seizures during weaning, nonconvulsive status epilepticus, lethargy, constipation, worsening chronic cholecystitis Devinsky et al., 2018 [75]
Oral CBD Dose Simultaneous Drug Administration Reported Adverse Effects (AEs) Refs.
Neurological studies
Double-blind, randomized, placebo-controlled trial Age 2-55; 171 patients with Lennox-Gastaut syndrome 20/mg/kg/day
(14 weeks)
Clobazam, valproate, lamotrigine, levetiracetam, rufinamide AEs in 62% patients (53/86); Moderate: diarrhea, somnolence, pyrexia, decreased appetite, vomiting; Severe: increased ALT concentration, increased AST concentrations, increased γ-glutamyltransferase concentrations Thiele et al., 2018 [65]
Ongoing expanded‐access program (EAP) Age 0.4-62
(average 13);
607 patients with treatment-resistant epilepsy
2-10 mg/kg/day increased to a maximum of 25-50 mg/kg/day; median duration 48 weeks Up to 10, including clobazam, lamotrigine, topiramate, rufinamide, valproate, levetiracetam, stiripentol, felbamate AEs in 88% patients; Moderate: diarrhea, somnolence, convulsions; Severe (33%): convulsions, status epilepticus, liver abnormalities (10%) Szaflarski et al., 2018 [66]
Psychiatric studies and psychiatric AEs
Double-blind, randomized CBD versus amisulpride trial Age 18-50; 42 patients with acute paranoid schizophrenia or schizophreniform psychosis 200 mg/day
increased to a maximum of 800 mg/day (28 days)
Lorazepam Fewer motor disturbances, weight gain, and sexual dysfunction than amisulpride Leweke et al., 2012 [38]
Meta-analysis of studies & reviews on CBD efficacy & safety in schizophrenia 57 patients with
300–600 mg Not reported Does not decrease anxiety; Frequent AEs (not reported) Guinguis et al., 2017 [62]
Double-blind, randomized, placebo-controlled trial Age 18-50; 32 patients with persecutory ideation and anxiety 600 mg Not reported AEs in 31% patients (5/16); Tiredness/sedation (n=5), lightheaded/dizziness (n=2), nausea (n=2), abdominal discomfort (n=1), increased appetite/hunger
(n=2); A strong trend toward increased anxiety was documented; no effect on persecution ideation
Hundal et al., 2018 [39]
Double-blind, randomized, placebo-controlled trial Age 18-65; 88 patients with no treatment-resistant schizophrenia or related psychotic disorder 1,000 mg/day (43±3 days) Not-specified
AEs in 35% patients (15/43) (similar as placebo); Moderate: diarrhea (n=4; placebo, n=2), nausea (n=3), headache (n=2, placebo, n=2) Mc Guire et al., 2018 [35]

3.1. Neurological Effects

3.1.1. In Vitro Neurological Effects

In vitro CBD toxicity was identified in Sprague Dawley rats’ oligodendrocytes, the cells responsible for CNS white matter myelination [59]. Following incubation with 100 nM-10 μM CBD for 20-30 min, a concentration-dependent decrease in oligodendrocyte viability was observed. The mechanism appeared to be through increases in intracellular Ca 2+ . If there was no extracellular Ca 2+ , CBD-induced cell death was reduced at 1 µM by 50.4%±18%. Furthermore, the disruption of mitochondrial membrane potential (MMP), and ROS production were reduced. CB1, CB2, TRPV1, adenosine A2A, PPARγ, ryanodine, and inositol triphosphate (IP3) receptor antagonists did not prevent CBD-induced intracellular Ca 2+ increase, suggesting that these receptors did not mediate these CBD actions. However, CBD toxicity at 1 µM was significantly impaired by caspase-inhibitors, poly(ADP-ribose) polymerase PARP-1 and calpain, suggesting caspase-dependent and -independent cell death pathway activation.

CBD’s neuroprotective effect was investigated in human neuroblastoma SH-SY5Y cells during and after neuronal differentiation [60]. Terminally-differentiated cells incubated with 2.5 µM CBD were not protected against ROS produced by exposure to glycolaldehyde, methylglyoxal, 6-hydroxydopamine, and hydrogen peroxide. During SH-SY5Y cell differentiation, CBD did not induce changes in antioxidant potential, nor neurite density. CBD exposure during neuronal differentiation may sensitize immature cells to redox-active drug neurotoxicity.

3.1.2. In Vivo Neurological Effects

In 1981, Rosenkrantz and Hayden investigated acute cannabinoid toxicity in rhesus monkeys following 150, 200, 225, 250, or 300 mg/kg intravenous (IV) CBD for 9 days [61]. The LD50 was 212 mg/kg CBD. Tremors were observed at all doses and CNS inhibition (depression, sedation, and prostration) was evident within 30 min.

There is considerable interest in the CBD treatment of schizophrenia. In a randomized, double-blind CBD versus amisulpride clinical trial (42 patients, CBD or amisulpride 200 mg/day increasing to 800 mg/day over 28 days), both treatments were shown to be safe and significantly associated with clinical improvement [38]. There were significantly fewer CBD AEs than for amisulpride, including fewer extrapyramidal symptoms (acute dyskinesias and dystonic reactions, tardive dyskinesia, Parkinsonism, akinesia, akathisia, and neuroleptic malignant syndrome). CBD treatment increased serum anandamide concentrations, possibly due to CBD inhibition of fatty acid amide hydrolase (FAAH).

McGuire et al. also found a low incidence (≥4%) of mild AEs including headache, with a frequency similar to placebo in schizophrenic patients [35]. However, a meta-analysis of CBD efficacy and safety in schizophrenia concluded that there was “moderate evidence” that CBD did not decrease symptoms and produced frequent AEs in patients, as measured by the PANSS, brief psychiatric rating scale (BPRS), and Stroop color-word test (SCWT) [62].

In 2017, Garberg et al. administered 50 mg/kg IV CBD to four piglets to evaluate drug safety and potential neuroprotective effects. CBD significantly reduced brain-derived neurotrophic factor (BDNF) expression and other signaling proteins in the hippocampus and frontal cortex with no effect in the striatum. It was concluded that CBD did not provide neuroprotection during early global hypoxia-ischemia [63]. However, in a study investigating possible treatments for neonatal hypoxic-ischemic encephalopathy, low 1 mg/kg IV CBD dose in combination with hypothermia, found neuroprotective effects and modulation of excitotoxicity and inflammation in newborn hypoxic-ischemic encephalopathy animal models [64].

The greatest success for CBD treatment is the reduction in seizures in children with refractive epilepsy. In a randomized, double-blind, placebo-controlled trial, CBD reduced atonic seizures in Lennox-Gastaut patients, who also received clobazam, valproate, lamotrigine, levetiracetam, or rufinamide [65]. Severe AEs occurred in 20 (23%) of 86 patients in the CBD group including sleep apnea. Twelve (14%) patients treated with CBD and one (1%) treated with placebo withdrew from the study.

Long-term CBD safety and efficacy were evaluated in children and adults with intractable epilepsies administered

up to 10 antiepileptic drugs including clobazam, valproic acid, levetiracetam, lamotrigine, stiripentol, rufinamide, topiramate, and felbamate [66]. The starting oral CBD dose was 2‐10 mg/kg/day, escalating to 25‐50 mg/kg/day for a median 48-week duration. Twenty-four percent of 607 patients in the safety dataset (mean age 13 years) withdrew, primarily due to failed efficacy (n=89, 61%) and AEs (n=32, 22%). AEs were reported in 88% of all patients, severe AEs such as convulsions and status epilepticus were reported for 33% of patients.

In the Epidiolex ® FDA approval notification [27] and Epidiolex ® prescription information [19], CBD’s in vivo AEs in humans included, similar to other anti-epileptics, suicidal thoughts, suicide attempts, agitation, depression, aggression, and panic attacks.

3.2. Changes in Behavior

Most clinical CBD research focused on reduction in seizures in patients with Dravet’s or Lennox-Gastaut syndromes. The most common AEs were sedation, somnolence, fatigue, lethargy, and malaise. In an online survey of 117 parents who administered CBD cannabis preparations to their children with uncontrolled epilepsy, the median dose was 4.3 mg/kg/day for a median duration of 6.8 months [67]. AEs were reported in 59% of children, but there were no controls. Porter and Jacobson reported similar findings in another smaller online survey including 18 parents [68]. Drowsiness and fatigue reportedly affected 37% and 16% of children, respectively. In a retrospective study of 74 children 1–18 years old with seizures, the CBD dose ranged from 1 to 20 mg/kg/day for more than 3 months (average 6 months) [69]. AEs were reported in 47% of children. Status epilepticus was attributed to the disease, and drowsiness and fatigue could have been due to the other administered anti-epileptic drugs, making it difficult to assign AEs to the CBD treatment.

From 2016-2018, Devinsky et al. investigated CBD efficacy for the treatment of Dravet syndrome and Lennox-Gastaut syndrome and reported associated AEs. In a 2016 open-label clinical trial of 214 patients 1-30 years old with treatment-resistant epilepsy, patients received up to 25-50 mg/kg/day CBD for 12 weeks [70]. Of the 162 patients in the safety and tolerability analysis, 79% reported AEs, 25% somnolence, 11% convulsions, and more than 5% reported somnolence, fatigue, lethargy, convulsions, status epilepticus, changes in concentrations of concomitant antiepileptic drugs, gait disturbance, and sedation. Serious adverse events were reported in 30% patients, including one unexpected death regarded as unrelated to study drug. Twelve percent had severe adverse events possibly related to CBD use, the most common (6%) was status epilepticus. Ten percent receiving the highest dose had to lower the dose prior to the end of the trial and 4% stopped treatment, most likely due to AEs. The median reduction in monthly motor seizures was 36.5% (IQR 0–64.7).

In a 2017, randomized, double-blind, placebo-controlled CBD trial on Dravet’s syndrome, 120 children received 20 mg/kg/day oral CBD or placebo for 14 weeks, in conjunction with their standard treatment (1 to 5 antiepileptic drugs) [71]. AEs occurred more frequently in the CBD than the placebo group, with somnolence (36% vs 10%) being the most common AE. Another less common AE was fatigue.

Adverse reactions were reported in 199 children and young adults treated with 2-5 mg/kg/day CBD for uncontrolled seizures [72] and in 424 children and young adults treated with 0.5-50 mg/kg/day CBD for refractory epilepsy [73]. The most common AEs were drowsiness, somnolence, and fatigue.

In a 3-week 2018 treatment trial in 4 to 10-year-old children with Dravet’s syndrome receiving 5, 10, or 20 mg/kg/day CBD, there were more AEs following CBD than placebo [74]. Children were concomitantly taking clobazam, valproate, levetiracetam, topiramate, and stiripentol. The most frequent AEs were somnolence, sedation, ataxia, and abnormal behavior.

In a 2018 randomized double-blind trial investigating CBD effect on atonic seizures in 225 patients 2-55 years old with Lennox-Gastaut syndrome, patients received 10 and 20 mg/kg/day oral CBD for 28 days [75]. In conjunction with other antiepileptic drugs, seizure frequency was reduced compared to placebo. This most common AE was somnolence. Serious AEs included somnolence and lethargy. Somnolence occurred more frequently in those receiving 20 mg/kg/day CBD than 10 mg/kg/day. AEs were reported in 6 patients following 20 mg/kg/day CBD, one following the lower dose, and one receiving a placebo.

In a randomized, double-blind, placebo-controlled trial, CBD was efficacious in reducing atonic seizures in patients with Lennox-Gastaut syndrome, also taking clobazam, valproate, lamotrigine, levetiracetam, or rufinamide [65]. Treatment-related AEs, including somnolence, were mostly mild and occurred in 62% of 86 patients treated with 20 mg/kg/day CBD for 14 weeks. Severe AEs included sedation occurring in 23% of 86 patients receiving CBD; 14% patients treated with CBD and one (1%) treated with placebo withdrew from the study.

Long-term CBD safety and efficacy were evaluated in an ongoing expanded‐access program in children and adults with treatment‐resistant epilepsies receiving up to 10 antiepileptic drugs including clobazam, lamotrigine, topiramate, rufinamide, valproic acid, levetiracetam, stiripentol, and felbamate [66]. The starting oral CBD dose was 2‐10 mg/kg/day, escalating to 25‐50 mg/kg/day for a median 48-week duration. Twenty-four percent of 607 patients in the safety dataset (mean age 13 years) withdrew, mostly for lack of efficacy (n=89, 61%) and AEs (n=32, 22%). Eighty-eight percent experienced treatment‐emergent AEs, with the most common AE being somnolence (22%).

In a study on the efficacy of CBD in schizophrenia, there was a low incidence (≥4%) of mild AEs including somnolence and insomnia, with a frequency similar to that found in placebo [35].

Several preclinical and clinical studies documented CBD’s acute anxiolytic effects [76-78], although more recently ElBatsh et al. demonstrated that 10 mg/kg intraperitoneal (IP) CBD over 14 days produced an anxiogenic effect in rats [79].

CBD AEs in humans reported in the Epidiolex ® FDA approval notification [27] and the Epidiolex ® prescription information [19] included somnolence, sedation and lethargy, insomnia, sleep disorder and poor quality sleep, fatigue, malaise, and asthenia.

3.3. Hepatic Effects

Following 90 days of oral CBD (30-300 mg/kg/day), liver and kidney weights in rhesus monkeys were 13-56% greater than controls, without morphological changes in the organs [61].

In 214 patients 1-30 years old with treatment-resistant epilepsy receiving up to 25-50 mg/kg/day CBD for 12 weeks, 7% had slightly elevated liver function tests, but one had a significant increase in transaminases (considered hepatotoxic), leading to CBD withdrawal [70]. All patients with hepatic or platelet abnormalities were also taking valproate. In a 3-week treatment trial in 4 to 10-year-old children with Dravet’s syndrome receiving 5, 10, or 20 mg/kg/day CBD and concomitant anti-epileptic drugs, 6 patients taking CBD and valproate developed elevated transaminases, but not liver injury [74]. In a 2017, double-blind, randomized, placebo-controlled CBD trial on Dravet’s syndrome, 120 children and young adults received 20 mg/kg/day oral CBD or placebo for 14 weeks, along with standard treatment of 1 to 5 antiepileptic drugs [71]. AEs occurred more frequently in the CBD than placebo group including increases in liver-function tests. Patients with Lennox-Gastaut syndrome (n=225) receiving 10 and 20 mg/kg/day oral CBD for 28 days, reported serious AEs with elevated aspartate aminotransferase (AST), alanine aminotransferase (ALT), γ-glutamyltransferase (GGT) concentrations, and worsening chronic cholecystitis [75]. The most common AE was AST or ALT increases 3.2-12.2 times the upper limit of normal in 4 of 6 patients receiving 20-mg/kg/day CBD, one receiving 10-mg/kg/day CBD, and among patients concomitantly receiving valproate (79%, 9 in the 20 mg/kg/day group and 2 in the 10 mg/kg/day group). Overall, 9% receiving CBD had

elevated liver AST concentrations and none in the placebo group. Severe AEs in Lennox-Gastaut patients receiving CBD treatment included increased ALT, AST, and GGT concentrations [65]. In children and adults with treatment‐resistant epilepsies receiving up to 25‐50 mg/kg/day for a median 48-week duration, AEs related to ALT/AST abnormalities (higher than three times the upper limit of normal) were reported for 10% of patients; 75% of these also received valproate [66].

CBD AEs in humans presented in the Epidiolex ® FDA approval notification [27] and Epidiolex ® prescription information [19] include transaminase elevation (especially with concomitant valproate). Epidiolex ® can also cause liver injury, usually mild, but more severe injury with related symptoms such as jaundice can occur although rarely.

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3.4. Gastrointestinal Effects

In an online survey of 117 parents who administered a median CBD-enriched cannabis preparation of 4.3 mg/kg/day for a median duration of 6.8 months for treatment of their children’s epilepsy, 59% reported AEs, primarily gastrointestinal disturbances; however, there was no control group [67]. In a retrospective study of 74 patients, age range 1-18 years, CBD dosage ranged from 1 to 20 mg/kg/day for more than 3 months (average 6 months), 47% AEs were reported, prominently [69]. Gastrointestinal disturbances could be due to other co-administered anti-epileptic drugs making it difficult to assign responsibility to CBD.

In 162 participants included in a clinical trial of 25-50 mg/kg/day CBD for 12 weeks for treatment-resistant epilepsy, serious AEs included diarrhea, weight loss, and gastrointestinal intolerance (n=1) [70]. In a CBD trial on Dravet’s syndrome, 120 children and young adults were randomly receiving 20 mg/kg/day oral CBD or placebo for 14 weeks, AEs included diarrhea (31% vs 10%), loss of appetite (28% vs. 5%), and much less commonly vomiting [71]. Diarrhea and weight and appetite loss were also reported in 199 children and young adults treated with 2-5 mg/kg/day CBD for uncontrolled seizures [72], and in 424 children and young adults treated with 0.5-50 mg/kg/day CBD for refractory epilepsy [73].

Similarly, in 4 to 10-year-old children with Dravet’s syndrome, CBD treatment with 5, 10, or 20 mg/kg/day reported appetite loss and vomiting as the most frequent AE [74]. Devinsky et al. reported AEs of decreased appetite, diarrhea, and vomiting, and a serious AE constipation in 2 to 55-year-old patients (n=225) with Lennox-Gastaut syndrome, receiving 10 and 20 mg/kg/day oral CBD for 28 days [75]. Decreased appetite and diarrhea occurred more frequently in the high-dose group than the low-dose group (10 mg/kg/day). CBD significantly reduced atonic seizures in patients with Lennox-Gastaut syndrome, with mostly mild AEs diarrhea, decreased appetite, and vomiting in 62% of 86 patients treated with 20 mg/kg/day CBD for 14 weeks [65]. Vomiting was among the severe AEs reported.

Following 25‐50 mg/kg/day for a median of 48 weeks in children and adults with treatment‐resistant epilepsies, 88% of all patients experienced treatment‐emergent AEs and 33% experienced severe AEs, including vomiting [66]. The most common AEs were diarrhea (29%), and decreased appetite 12%). In clinical studies of schizophrenia, mild AEs, diarrhea and nausea, occurred with a low incidence of ≥4%, with a frequency similar to placebo [35].

CBD AEs in humans listed in the Epidiolex ® FDA approval notification [27] and in Epidiolex ® prescription information [19] include decreased appetite, diarrhea, nausea, vomiting, and abdominal pain.

3.5. Drug-drug Interactions

CBD’s interaction with CYP enzymes can reduce or potentiate the effects of other drugs [19, 22, 80]. In 1974, Karniol et al. investigated effects of oral 0, 15, 30, and 60 mg CBD alone, 0 and 30 mg THC alone, and CBD and THC combinations to study potential drug-drug interactions in a double-blind trial in 40 healthy male volunteers [81]. THC alone disturbed time estimations, increased pulse rate, and induced strong psychological reactions, while up to 60 mg CBD alone produced no effects. Thirty to 60 mg CBD weakened or blocked time production impairment, psychological disturbances, and pulse rate acceleration produced by THC, when co-administered. CBD also decreased anxiety following THC, with subjects reporting more pleasurable effects.

In 1995, CBD effects on THC pharmacokinetics were investigated in mice receiving 120 mg/kg IV CBD 2 h before 12 mg/kg IV THC [82]. CBD inhibited hepatic microsomal THC metabolism reducing THC clearance. 7-OH-THC and 6α-OH-THC concentrations were increased in brain, with few changes in blood. CBD-induced changes in metabolite profile and brain pharmacokinetics might change pharmacological effects. Bergamaschi reviewed research on animal models in 2011 showing that CBD did not induce changes in food intake, catalepsy, or physiology in rats and mice [57]. Chronic low and high CBD doses inhibited hepatic drug metabolism producing drug-drug interactions in vivo in mice and rats following 10-120 mg/kg IP CBD [83-93]. However, more recently, when equal amounts of CBD and THC were co-administered, CBD did not modify THC blood concentrations in humans [94]. In addition, Karschner et al. found no changes in THC’s subjective and physiological effects when equivalent doses of THC alone or CBD and THC (Sativex ® ) were given via oromucosal spray [95].

In a clinical trial of treatment-resistant epilepsy, 162 participants included in the safety and tolerability analysis received 25-50 mg/kg/day CBD for 12 weeks and sustained changes in concentrations of concomitant antiepileptic drugs that may have led to status epilepticus [70]. Similarly, in patients with CBD-reduced atonic seizures, severe AEs increased concomitant antiepileptic concentrations in 23% of 86 patients in the CBD group; 14% of patients treated with CBD and one (1%) treated with placebo withdrew from the study [65].

THC, CBD, and THC and CBD effects via vaporization of 20 mg THC, CBD, or 1:1 THC:CBD, oral, and subcutaneous (SC) administration of 10 mg/kg THC or CBD, or 20 mg/kg 1:1 THC:CBD, or oral gavage were investigated in Wistar rats [96]. Although no statistical analyses were performed, SC CBD inhibited THC metabolism resulting in 4 times higher serum and brain THC concentrations when CBD and THC were simultaneously administered compared to THC alone. Serum and brain CBD concentrations were half the concentration when CBD and THC were co-administered compared to CBD alone. Oral CBD inhibited THC metabolism with 2 to 3 times higher serum and brain THC concentrations and two-fold lower serum and brain CBD concentrations when CBD and THC were administered together. CBD did not inhibit THC metabolism after pulmonary THC and CBD administration. SC cannabinoids administration (THC and CBD and THC and CBD alone) produced hypolocomotion. Oral THC and THC and CBD produced almost total immobility, but oral CBD produced mild hyperlocomotion. The apparent CBD inhibition of THC metabolism after oral and SC administration had little impact on THC-induced behavior.

In a CBD versus amisulpride trial, 42 patients significantly improved seizure control, with significantly higher serum anandamide concentrations, perhaps due to CBD inhibition of the enzyme FAAH [38].

Epidiolex ® and concomitant clobazam administration, produced a 3-fold increase in plasma concentrations of N-desmethylclobazam, the active metabolite of clobazam, increasing the risk of AEs such as excessive sedation [19, 97]. Epidiolex ® increases plasma concentrations of drugs metabolized by CYP2C19 such as diazepam or clobazam.

In 137 patients in the efficacy analysis receiving 25-50 mg/kg/day CBD for 12 weeks for treatment-resistant epilepsy, 11 withdrew due to AEs including allergy to sesame oil vehicle (n=1) [70]. In the Epidiolex ® FDA approval notification [27] and in Epidiolex ® prescription information [19], CBD AEs in humans included allergic reactions and rash.

3.6. Respiratory Effects

In 162 patients with treatment-resistant epilepsy receiving 25-50 mg/kg/day CBD for 12 weeks, a serious AE of pneumonia was reported [70]. In a trial investigating the effects of 10 and 20 mg/kg/day oral CBD for 28 days on atonic seizures in 2 to 55-year-old patients with Lennox-Gastaut syndrome (n=225), common AEs included upper respiratory tract infection [75]. In children and adults with treatment‐resistant epilepsies receiving up to 25‐50 mg/kg/day for a median 48-week duration, 33% experienced severe AEs including pneumonia [66]. The most common AEs were upper respiratory tract infection in 12%.

CBD AEs in humans in the Epidiolex ® FDA approval notification [27] and in the Epidiolex ® prescription information [19] included viral, fungal, and pneumonia infections.

3.7. Pyrexia

The most frequent AE was pyrexia in a 3-week treatment trial of 5, 10, or 20 mg/kg/day CBD in 4 to 10-year-old children with Dravet’s syndrome [74]. In the same manner, 2 to 55-year-old patients with Lennox-Gastaut syndrome (n=225), receiving 10 and 20 mg/kg/day oral CBD for 28 days for atonic seizures had pyrexia amongst common AEs [75]. Treatment-related AEs were mostly mild and occurred in 62% of 86 patients treated with 20 mg/kg/day CBD for 14 weeks, including pyrexia in patients with Lennox-Gastaut syndrome, with concomitant clobazam, valproate, lamotrigine, levetiracetam, or rufinamide [65].

3.8. Cardiovascular Effects

After rhesus monkeys received 150, 200, 225, 250, or 300 mg/kg IV CBD for 9 days, higher CBD doses elicited hypopnea, bradycardia, and cardiac failure [61]. In 162 patients with treatment-resistant epilepsy administered 25-50 mg/kg/day CBD for 12 weeks, serious AEs included diarrhea, weight loss, and gastrointestinal intolerance (n=1) [70]. Five (3%) patients experienced mild to moderate and one case of severe thrombocytopenia, resolving after stopping valproate. One patient also taking valproate developed hyperammonemia leading to stopping CBD intake. AEs were clearly related to dose and anti-epileptic drug intake. All patients receiving CBD and valproate had liver or blood abnormalities.

CBD was evaluated as a neuroprotectant after perinatal hypoxia-ischemia in piglets [63]. Piglets were randomized to 50 mg/kg IV CBD (n=13) or vehicle (n=9). CBD induced severe hypotension in two piglets; one suffered fatal cardiac arrest (50 mg/kg, IV). CBD (25 mg/kg, n=4) induced significant hypotension in one piglet, while 10 mg/kg (n=5) was well tolerated. A significant negative correlation between plasma CBD concentration and blood pressure during drug infusion was observed (p<0.005).

3.9. Reproductive Effects

3.9.1. In Vitro Reproductive Effects

In 1982, the effects of 100-200 µM CBD reduced the basal accumulation of progesterone, testosterone, and estradiol-17β in preovulatory rat follicles by up to 60% [98]. Luteinizing hormone-stimulated increase in progesterone and testosterone was reduced by 75-88% following 50-200 µM CBD and estradiol-17β accumulation was inhibited by 40%.

Progesterone 17α-hydroxylase activity was significantly inhibited by 100-1000 µM CBD [99]. Testosterone 6β and 16α-hydroxylase activity and androstenedione formation from testosterone in rat liver microsomes also were significantly reduced by CBD.

3.9.2. In Vivo Reproductive Effects

Following oral 30, 100, and 300 mg/kg CBD for 90 days in rhesus monkeys, significant 57% decreases in testicular weights were observed after 200 mg/kg CBD that continued after the end of treatment [61]. Similarly, acute and subchronic 0.6, 0.8, and 1.2 mg/kg smoked CBD exposure in rats showed a severe dose-related seminiferous tubule degeneration with interference in sperm maturation [100]. In addition, testicular weight decreases correlated with a dose-related inhibition of spermatogenesis.

In 42 patients administered 200 mg/day gradually increased to 800 mg/day CBD or amisulpride over 28 days, there were significantly fewer CBD-related AEs compared to amisulpride, including lower prolactin release, and less sexual dysfunction [38].

Fertility also was affected by CBD. In sea urchins, in vivo fertilization was inhibited by 0.1-100 μM CBD due to a decreased acrosome reaction in sperm [101, 102].

When pregnant rats were administered 0, 75, 150, or 250 mg/kg/day oral CBD during organogenesis, developmental toxicity including increased embryofetal mortality at the highest dose was observed [103]. Oral 0, 50, 80, or 125 mg/kg/day CBD administration during organogenesis in pregnant rabbits decreased fetal body weights and increased fetal structural variations were shown following the highest dose [103]. Also, following 150 and 250 mg/kg/day oral CBD to pregnant and lactating rats, decreased growth, delayed sexual maturation, neurobehavioral changes with decreased activity, and AEs for male reproductive organ development and fertility in offspring were noted. No maternal toxicity was reported [103].

When Swiss mice received 30 mg/kg oral CBD or placebo in sunflower oil for 34 consecutive days, CBD decreased total circulating testosterone by 76% (still within normal ranges), significantly increased abnormalities in spermiation and meiotic stages [104]. CBD-treated mice had a 38% reduction in spermatozoa in the epididymis tail and more head abnormalities in the sperm and cytoplasmic droplets in the flagella medial region.

3.10. Cellular Effects

In vitro toxicity was observed in the production of cytokines in human eosinophil leukemia cells, peripheral blood mononuclear cells, human T-lymphotropic virus-1 (HTLV-1) positive B cells, and T cells following 1-10 μg/mL CBD [105]. CBD suppressed T-cell activities in splenocytes exposed to CBD in vitro or isolated from CBD-administered mice [106]. Exposure of splenocytes to CBD produced ROS, reduced cellular glutathione (GSH) content, and significantly stimulated caspase-8 activation. Pretreatment with a caspase-8 inhibitor significantly reduced, in a concentration-dependent manner, CBD-mediated apoptosis, but not ROS production, suggesting that CBD’s apoptotic effects in primary lymphocytes are associated with oxidative stress-dependent activation of caspase-8.

In vitro apoptosis was induced in mouse thymus and spleen cells exposed to 4-16 μM CBD [106, 107], and a pro-apoptotic effect was noted in lymphocytes following 10 mg/kg IP CBD [106].

ATP-binding cassette transporter (ABC) ABCG2 activity in mouse embryonic fibroblasts was reduced after in vitro exposure to 10-50 µM CBD [108].

Following exposure to 3-100 μM CBD, in vitro P-glycoprotein activity was reduced in human T lymphoblastoid leukemia cells [109]. In addition, ABCC1 transporter was inhibited in human ovarian carcinoma cells with a CBD IC50 of 128.3 μM [110]. CBD was also shown to interact with P-glycoprotein efflux transporters involved in multidrug resistance [111] and may also affect placental permeability and pharmacokinetics of other drugs. In humans, 600 mg of the antibiotic rifampicin, a CYP3A4 inducer involved in CBD metabolism, significantly reduced peak plasma CBD from 1.0 to 0.50 µg/L (-52%), while antifungal ketoconazole (400 mg), a CYP3A4 inhibitor, almost doubled peak plasma CBD from 0.7 to 1.3 µg/L (+89%) [112].


This is an exciting time for CBD research and medicine. Epidiolex ® , containing 98% CBD, was approved by the FDA for the treatment of intractable epilepsy in patients with Dravet’s or Lennox-Gastaut syndromes, showing that a plant extract containing primarily CBD can provide the reproducibility needed for pharmacotherapies. There is active in vitro and preclinical research into the mechanisms of action of CBD in efforts to better understand its pharmacodynamics and pharmacokinetics and therapeutic potential. Clinical research is proceeding for multiple indications for CBD in well-designed, randomized, placebo-controlled clinical trials, by a variety of routes of administration. Pharmaceutical companies pursue synthetic CBD and plant extracts as CBD sources. CBD may provide a new approach as a stand-alone-drug and as an adjunct to other medications for unmet clinical needs.

Amongst all of these positive developments, unapproved CBD products are being sold across the US and in other countries without rigorous standardization of CBD potency, the content of other constituents, and with unproven claims of health effects. Now that Epidiolex ® is approved, it is likely that off-label prescriptions will increase. It is important that physicians and patients understand that CBD, like any other medication, is not appropriate for every individual and every disease and that it has side effects that are not negligible and must be considered prior to use.

The most important consideration is whether or not there is sufficient scientific data that CBD is efficacious in treating a patient’s disease or condition. The field is changing rapidly, but proof of efficacy is limited currently to CBD as an anti-epileptic. A second critical factor is dose, route, and frequency of administration. In many of the preclinical studies, much higher CBD concentrations were administered. For example, many of the cardiovascular, hepatocellular damage, inhibition of P450 systems, hormone changes, decreased fertility, alterations of in vitro cell viability, and reduced P-glycoprotein activities effects occurred at doses of >200 mg/kg/day [61], far above the current up to 50 mg/kg/day doses suggested in recent anti-epileptic clinical studies. However, in the clinical trial data to date, few cardiovascular and reproductive effects were reported. Other in vivo preclinical studies utilized lower doses similar to those used in humans, but the route of administration, IP or IV, provided higher bioavailability and hence, a greater chance of AEs and toxicity.

Drug interactions are an important issue to be carefully considered when prescribing CBD. CBD is often added to a regimen of other medications, especially other anti-epileptics and the potential for drug-drug interactions could lead to serious health consequences. In vitro and in vivo data suggest that CBD interacts with pharmaceuticals, specifically drugs metabolized by the liver. Drug-drug interactions with CYP1A2 substrates (theophylline, caffeine), CYP2B6 substrates (bupropion, efavirenz), UGT1A9 (diflunisal, propofol, fenofibrate), UGT2B7 (gemfibrozil, lamotrigine, morphine, lorazepam), and clinically significant interactions with CYP2C8 and CYP2C9 (phenytoin) substrates occur when co-administered with Epidiolex ® [19].

In humans receiving the drug for the treatment of epilepsies and psychiatric disorders, the most common AEs included tiredness, diarrhea, nausea, and hepatotoxicity. Overall, the incidence of these occurrences is low and, in comparison with other drugs employed for the treatment of these diseases, CBD has a better side effect profile.

The length of treatment is another important factor because data on AEs is much more limited following chronic CBD administration. Research is still needed on larger cohorts of CBD patients, and evaluation of CBD effects following long-term exposure on genotoxicity and cytotoxicity, hormones, and the immune system are needed.

Two of the common AEs after CBD administration are somnolence and sedation [19, 65, 70, 73]. These effects are dose-related and potentiated by co-administration of the anti-epileptic drugs including clobazam and valproate, and other CNS depressants (including alcohol). Patients should be advised that their ability to drive or operate machinery could be impaired while under CBD treatment.

From the patient’s point of view, it is particularly important to consider the proportions of THC and CBD in cannabis products when used for medical or recreational purposes, since self-medicating with cannabinoid products may expose patients to products with inaccurate labeling, containing impurities, underdosing or overdosing, insufficient supply, and risk of AEs and drug-drug interactions [41, 97]. This variability in CBD formulations (tablets, oromucosal spray, oral capsules, vaporized cannabis plant material, powder in oil, and CBD-THC products), and the wide CBD dose range (18-1500 mg) influence CBD efficacy and AEs [80].

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In conclusion, possible factors contributing to CBD AEs are CBD potency, route of administration (vaporized, transdermal, oral), concurrent licit and illicit drug use, and drug-drug interactions.


The authors thank Simonetta Di Carlo, Antonella Bacosi, Laura Martucci, and Michele Sciotti. Oronzo Persano is acknowledged for technical help.

Are There Side Effects to CBD Oils, Pills, or Gummies?

The increasing prevalence of hemp-derived cannabidiol (CBD) products has necessitated the spread of information regarding its properties and — most importantly — whether it can be harmful. If you are brand new to the industry and looking to try something new, you are probably wondering: are there side effects to CBD oils, pills, or gummies? Thankfully, CBD is considered to have a very high safety profile, but like any substance with the ability to change brain chemistry, its use can result in potential side effects.

CBD is one of hundreds of compounds that are found in the cannabis plant, known as cannabinoids. These specialized molecules are designed to interact with specific internal receptors that are found throughout our brain and body. These cannabinoid receptors can influence many different processes regarding the modulation of other body systems, which is why people are affected when they consume cannabinoid compounds.

The Most common side effects of cbd

Those who are just learning about CBD may not realize that it does not have the ability to make you intoxicated. Tetrahydrocannabinol, or THC, is the only compound in cannabis that is capable of doing that. This is why hemp is ideal for extracting CBD oil, because it contains only trace amounts of THC, so users will not experience inebriation after its consumption.

However, several clinical trials have shown that patients who were treated with high doses of CBD (In some cases, over 1,300mg in a single day) had reported symptoms that ranged from mild to moderately severe, although nothing significantly life threatening. Research has so far indicated that the most common side effects of CBD can include things like queasiness, anxiety, fatigue, gastrointestinal issues, trouble with balance, dry mouth, and fluctuations in appetite or weight.

Nausea or vomiting

One reported side effect of CBD use is nausea, or vomiting. This can result from taking too high of a dose, which can be a different amount for each person as it is based on their individual biochemistry. For some new users, they may have trouble digesting the oil, which could potentially lead to an upset stomach.

When first trying out a CBD product, it is best to begin with the smallest dose possible, and work your way up. It is also important to note that when taking a tincture, it is necessary to hold the oil underneath your tongue for at least 1-2 minutes, or until the oil has been completely absorbed by the sublingual gland. In this way, the compounds are able to bypass the digestive system and go directly into the bloodstream.


Although many studies are currently underway to determine whether CBD helps with anxiety, some patients have indicated that it actually triggered rather than relieved their anxiety. This could be due to an overly high dose, although the quality of the CBD oil can have a huge effect as well. It may also correspond to the causes of individual stress or anxiety, whether they are due to external factors regarding lifestyle or internal body mechanisms that involve brain chemistry.


There has been a lot of research compiled regarding the use of CBD as a sleep aid, which makes sense as some users have reported excessive fatigue and tiredness associated with larger doses.


A small percentage of users experienced gastrointestinal issues like diarrhea after consuming CBD. This may also be due in part to the carrier oil that is used as a preservative in CBD products. Different types of carriers can include olive oil, coconut oil, avocado oil, or propylene glycol, and some people might be sensitive to a particular type.


Although there have been a few instances of dizziness associated with CBD use, this may also be an effect of gastrointestinal issues due to sensitivity of other ingredients. This is why it is very important to research all of the ingredients for a particular product, in case of allergies or other components that may cause a reaction.

Dry Mouth

Because CBD oil can be absorbed through the sublingual gland, cannabinoids have the potential to influence saliva production. However, if a CBD product causes excessive dry mouth, it may also be an indication of higher amounts of THC, which is primarily associated with this kind of symptom.

Always check the batch lab reports of a particular product to ensure that it does not have more than 0.3% THC. Some states have allowed for medical use of CBD products that contain more than the federal maximum amount of THC, so that is definitely something to consider and be aware of.

Changes in Appetite or Weight

Some consumers say they have experienced changes in their appetite or weight after using a CBD product. Cannabis products are often used in palliative care for terminal patients as a way to stimulate appetite, and this is considered one of the most common side effects of cannabinoids.

When cbd side effects may occur

It has become so popular in part because of its high safety profile, but when CBD side effects may occur can depend on the quality of the CBD product being consumed. Unfortunately, there are a lot of disreputable companies out there who are looking to make a quick buck in such a fast growing industry. This means they possibly use inferior processes for extracting the oil — some techniques involve the use of harsh chemicals which strip the plant of its natural components, and these processes could potentially leave behind trace amounts of toxic compounds. Currently, CO2 extraction is considered one of the cleanest and most efficient methods for extracting CBD oil.

It is important when choosing a CBD product to ensure that the company provides independent lab tests to confirm the purity of the oil, and to make sure that it does not contain higher amounts of THC, which is federally illegal. Many companies may not want to pay for this, which can be a disadvantage because not all batches of oil will come out with the same concentrations of cannabinoids, and it is important to follow these guidelines in order to ensure that only minimal amounts of THC are in the product.

Is CBD fda approved?

So, is CBD FDA approved? Currently, the Federal Drug Administration is still weighing in on CBD, and has not yet approved its medical use. Part of the issue is the expensive involved with clinical trials, which can cost millions of dollars.

There has been significant confusion within the industry because while hemp products and CBD are federally legal through the 2018 Farm Bill, the FDA has yet to approve their inclusion as an ingestible health supplement. However, FDA officials are aware of the high demand and pervasive use of CBD products, which has prompted them to request users, health practitioners, and industry experts to give their own experiences and comments regarding this issue. They held the first in a series of hearings in the summer of 2019, where people were invited to share their views, and they had also maintained a public comment forum on the FDA website where people were encouraged to give their thoughts on the matter.

It is believed that it will only be a matter of time before the FDA officially approves CBD, but many feel the process is taking too long. The fact that there are no established guidelines means that less scrupulous companies are able to operate with minimal oversight, which ultimately puts consumers at risk.

It is important to continue pressuring the FDA to make significant progress with regard to this decision, and hemp advocates continue to pursue legal avenues that would force them to speed up the process. Until then, both companies and customers will be at risk from the unstable regulatory landscape.

CBD: Benefits, Types, & Side Effects

CBD, or cannabidiol, is recommended for everything from anxiety and stress to indigestion and depression. And, a lot of people are using it. A recent Gallup poll found 1 in 7 adults in the U.S. has used CBD.

So, does it help? Studies of CBD are ongoing, but some benefits have been found.

What is CBD?

CBD is an herbal remedy – a treatment that comes from a plant, in this case, it is the cannabis sativa plant. Cannabis sativa has been used for thousands of years for both its healing and mind-altering effects.

There are two types of cannabis sativa: hemp and marijuana. The hemp plant is the source of CBD used in most products.

Hemp and marijuana plants

CBD Defined

CBD is one of a group of substances called cannabinoids derived from the cannabis sativa plant.

There are dozens of cannabinoids, as well as other substances, in cannabis sativa.

CBD is the primary cannabinoid in hemp. It has various healing properties. For example, it seems to lessen inflammation, the body’s response to illness or injury. In this way, it may help treat many different diseases.

CBD is not psychoactive; it does not have a mind-altering effect.


To better understand CBD, it helps to contrast it with tetrahydrocannabinol (THC). Many people are familiar with THC. It is the best known of the cannabinoids. THC was identified long before CBD. THC is the substance in marijuana that causes the high.

Marijuana contains more THC than CBD. Hemp has a very small amount of THC, less than 0.3 percent, and not enough to cause a high. As of 2018, CBD from hemp became legal in the U.S. with the Food and Drug Administration (FDA) maintaining control.

CBD’s main property is healing and it’s derived from the hemp plant. On the other hand, THC’s main property is mind-altering and it’s derived from the marijuana plant.

Excessive and continued use of CBD may lead to side effects, including memory loss, slow reaction time, and changes in mood such as irritability.

How CBD Works

As stated above, CBD is in a class of chemicals called cannabinoids. Because it comes from a plant, it is further classified as a phytocannabinoid.

The human body also produces natural cannabinoids, called endocannabinoids.

Both variations of cannabinoids act on cannabinoid receptors. These receptors are part of the complex endocannabinoid system (ECS). The system regulates the release of neurotransmitters (chemicals that communicate between nerve cells) in the brain, as well as in other parts of the nervous system. The ECS responds to both types of cannabinoids, phyto- and endo-.

By acting on the ECS, CBD may have many different effects on the body. Examples include: balancing the body’s overall physical functions (homeostasis), reducing pain sensation, and lessening the body’s reaction to injury or inflammation.

Medical Uses of CBD

CBD has been recommended for many different purposes, some of them tested, and some not. The prescription drug Epidiolex is the only CBD product approved by the FDA. It may be prescribed to treat two rare seizure disorders, or types of epilepsy, in children and adults.

Studies are ongoing, but some results show that CBD may be effective in reducing anxiety/stress and chronic (long-term) pain like back pain. It may also be effective for insomnia, or trouble sleeping.

There are studies of oral, topical, and inhaled CBD products for use in many other conditions, including dystonia (movement disorder), Fragile X syndrome (rare genetic disorder), graft-versus-host disease (bone marrow transplant rejection), multiple sclerosis (MS), opioid withdrawal, schizophrenia, and smoking cessation. CBD is also used to alleviate symptoms associated with Parkinson’s disease, but some study results advise against it.

Types of CBD Products

CBD products can be used by mouth (oral/edible) or applied to the skin (topical). These products have different concentrations of CBD.

CBD oil may be used both ways.

Other oral products include edible gummies and capsules. Topical CBD products may also be found in lotions, creams, or balms. Again, they are available in various concentrations.

CBD Dosage

The proper dosing of CBD for different conditions is still being studied, so new information is continuing to become available.

CBD should be used according to the manufacturer’s instructions. Make sure you read and follow the label carefully. Only use the amount instructed. Using more may increase the chance of side effects, interactions, or other problems.

The dose of a CBD product depends on the form and strength, as well as the concentration of CBD in it. It’s also based on whether or not it has other active ingredients.

Side Effects and Interactions of CBD

Common CBD side effects include: drowsiness, dry mouth, vomiting, decreased appetite, weight loss, and abnormal liver function blood tests.

INTERACTIONS: Check with your doctor or pharmacist before taking CBD with other medications. CBD may interact with some commonly prescribed medications including warfarin, lithium, sertraline, tramadol, codeine, captopril, and valproic acid and carbamazepine (both are anti-seizure medications).Fatty foods may increase the absorption of CBD.

CAUTIONS: People with liver problems or Parkinson’s disease should not take CBD.

Do not use CBD with medicines that are prescribed to control seizures or epilepsy (e.g. valproic acid or carbamazepine).

CBD may increase drowsiness when taken with other sedating medicines or herbal products.

Medical Research

Oral CBD for Pain

Research on the safety and effectiveness of oral CBD for pain is ongoing. Some of the research includes:

The National Academies of Sciences (NAS) found significant evidence that cannabis was an effective treatment for long-term (chronic) pain. However, much of the research was done outside of the U.S. And the forms of cannabis studied in the U.S. were not the same as those commonly used.

Reviews and meta-analyses of cannabinoids found the following:

Studies looked at the use of cannabinoids (THC alone and CBD combined with THC) in people with chronic pain. In general, results showed improvements in pain measures, but they were not statistically significant.

Studies found evidence, although not high-quality, that cannabis-based medicines reduced long-term nerve (chronic neuropathic) pain. All but two studies used plant-based THC/CBD mouth spray products (the other two used synthetic oral THC products).

Results of observational studies and randomized controlled trials (RCTs) of the effectiveness of cannabinoids in chronic non-cancer pain showed a 30% reduction in pain in 1 out of 3 of those using cannabinoids. These results were considered significant.

Topical CBD for Pain

There is also continuing research on the safety and effectiveness of topical CBD. Some of the research includes the following:

Although not in humans, an animal study found transdermal CBD had the ability to lessen the pain and inflammation of arthritis.

Topical cannabidiol oil was studied in 29 people with lower limb peripheral neuropathy. After using the oil for 4 weeks, results showed less intense and sharp pain and fewer other uncomfortable sensations.

Applications of transdermal cannabidiol were studied in people with temporomandibular (joint of the jaw) disorders (TMD) that caused myofascial (coverings of muscle) pain. Those studied had less muscle tension and pain after applying the topical CBD for 2 weeks.

Oral CBD to Help with Sleep

Oral CBD products may be used to help with sleep. This research includes the following:

Early results of research suggest that a 160mg dose of cannabidiol before bed significantly improves sleep duration compared to a placebo in patients with insomnia. Smaller doses did not have this effect. Also, patients did not feel drowsy the next morning.

Early research on CBD for the treatment of insomnia suggests that it may be effective. Additional studies are needed.

Animal studies of CBD found increased total sleep and improved sleep quality when sleep issues were associated with anxiety/stress.

Medical cannabis users reported they used cannabis with higher CBD and lower THC concentrations for their insomnia. They also reported a decrease in the time required to fall asleep.

A review and meta-analysis of 8 studies with low-quality evidence of cannabis-based medicines found that they were better at reducing sleep problems compared to inactive medicines (placebo).

A review of clinical trials of the effect of cannabinoids on sleep suggested that cannabinoids could improve sleep quality, decrease sleep disturbances, and decrease the time it takes to fall asleep. However, there were limiting factors, such as the small size of the studies.

An app was used to measure changes in insomnia in over 400 people taking medical cannabis. Results showed an average symptom severity reduction of 4.5 points on a 10-point scale, a significant improvement in insomnia.

Another review with meta-analysis of 104 studies evaluated cannabinoids for the treatment of chronic non-cancer pain. Within this review and analysis, the effect of cannabinoids on sleep was also examined. There was low-quality evidence of improved sleep.


The takeaway is that the initial research of CBD is promising but there is still much to learn. It may help with some conditions like long-term pain and sleep.

Because it is so widely available and recommended for so many problems, it must be used carefully and purchased from reliable sources.

CBD is just one of many supplements that can alleviate back pain or insomnia. Take a Goodpath assessment for an integrative program that incorporates supplements, nutrition, mind-body therapies, and exercise.

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