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Research · Supplements

CBD

At 10 to 20 mg/kg a day, prescription CBD cut seizures more than placebo in two rare childhood epilepsies. Fifteen of 16 pain trials found no benefit over placebo. Pooled trials link CBD to liver enzyme rises, including 5.6% of healthy adults at 5 mg/kg a day. Only 31% of products sold online matched their labels.

Add to Bio HackChecked 2026-11-09
Status
Sold in the US as hemp-derived products. Prescription cannabidiol (Epidiolex) is FDA-approved for seizures in Lennox-Gastaut syndrome, Dravet syndrome and tuberous sclerosis complex. FDA stated in January 2023 that existing food and supplement frameworks are not appropriate for CBD.
Also called
cannabidiol, CBD oil, hemp extract, full-spectrum CBD, broad-spectrum CBD, CBD gummies, Epidiolex, Epidyolex
Taken for
anxiety, sleep, pain, stress, inflammation, recovery, seizures

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help2

Reported risks6

What people take it for, and what was found

Shown to help2

Strong

Seizures in Dravet and Lennox-Gastaut syndromes

Shown to cut seizures in Dravet and Lennox-Gastaut syndromes, with drop seizures falling about 42% against 17% to 22% on placebo. These trials used prescription CBD.

The numbers and sources
Effect
In 120 children and young adults with Dravet syndrome, 20 mg/kg a day for 14 weeks cut median monthly convulsive seizures from 12.4 to 5.9, against 14.9 to 14.1 with placebo (adjusted median difference -22.8 percentage points, 95% CI -41.1 to -5.4) [1]. In 225 patients with Lennox-Gastaut syndrome, drop seizures fell by a median 41.9% at 20 mg/kg and 37.2% at 10 mg/kg, against 17.2% with placebo [2]. In a second Lennox-Gastaut trial of 171 patients, drop seizures fell 43.9% with 20 mg/kg against 21.8% with placebo (median difference -17.21, 95% CI -30.32 to -4.09) [3]. A 2026 meta-analysis of 7 RCTs (1,154 participants) found a pooled seizure frequency risk ratio of 0.72 (95% CI 0.71 to 0.73) against placebo, consistent across Dravet syndrome, Lennox-Gastaut syndrome and tuberous sclerosis complex. Transdermal CBD showed no short-term effect [4]. Across 46 studies (5 RCTs, 2,592 patients) in developmental and epileptic encephalopathies, 49.9% (95% CI 44.9 to 55.0) had seizures cut by half or more and 5.7% became seizure-free [5].
Population
Patients aged 2 to 55 with drug-resistant seizures, on top of existing antiepileptic drugs [1][2][3]. Patients with drug-resistant epilepsy [4] and developmental and epileptic encephalopathies of any age [5].
Sources
[1], [2], [3], [4], [5]
Caveats
All three pivotal trials were funded by GW Pharmaceuticals, the maker of Epidiolex [1][2][3]. Most studies in [5] were not randomized, and heterogeneity was substantial. They tested purified prescription CBD, not retail products. Seizure freedom was 5% vs 0% in Dravet syndrome (p = 0.08) [1].
Moderate

Anxiety

Shown to lower anxiety in people with anxiety disorders across 8 small studies, with a confidence interval close to zero.

The numbers and sources
Effect
A meta-analysis of 8 studies (316 participants) found CBD lowered anxiety (Hedges' g -0.92, 95% CI -1.80 to -0.04) across generalized anxiety, social anxiety and PTSD [6].
Population
People with anxiety disorders [6].
Sources
[6]
Caveats
Small total sample, and the authors urge caution [6]. The confidence interval runs close to zero.

Not shown to help3

Moderate

Pain

Not shown to relieve pain more than placebo in 15 of 16 trials of pharmaceutical-grade CBD across 12 pain conditions.

The numbers and sources
Effect
A 2024 review found 16 randomized trials of pharmaceutical-grade CBD with pain as an outcome, across 12 pain conditions, at 6 to 1,600 mg and from a single dose to 12 weeks. Fifteen of the 16 showed no benefit of CBD over placebo [7].
Population
Adults with a range of pain conditions [7].
Sources
[7]
Caveats
The review is not a pooled meta-analysis [7].
Limited

Inflammation markers

Limited evidence: CBD and THC trials found no significant change in IL-6, IL-8, IL-10 or TNF-alpha.

The numbers and sources
Effect
In a meta-analysis of randomized trials of CBD and THC, pooled changes in IL-6 (SMD -0.17, 95% CI -0.56 to 0.23), IL-8 (-0.30, 95% CI -0.62 to 0.01), IL-10 (-0.10) and TNF-α (-0.09, 95% CI -0.45 to 0.27) did not differ significantly from control [8].
Population
13 trials, with 2 to 4 trials and about 78 to 129 people per arm in each pooled marker [8].
Sources
[8]
Caveats
The review pooled CBD and THC interventions. GRADE certainty ranged from very low (IL-6) to moderate (IL-8, TNF-α) [8]. Blood markers, not symptoms.
Limited

Sleep

Small trials found CBD did not change total sleep time or significantly improve sleep disturbance, with a small gain in deep plus REM sleep in one.

The numbers and sources
Effect
In 125 people with insomnia, 300 mg of CBD with terpenes on at least 4 nights a week for 4 weeks raised the share of the night in slow-wave plus REM sleep by 1.3 percentage points over placebo (95% CI 0.1 to 2.5), measured by a wrist-worn tracker. Total sleep time did not change [9]. In 63 adults with high trait worry, 300 mg a day for 2 weeks did not improve sleep disturbance significantly more than placebo (p 0.10) [10].
Population
Adults with insomnia in a crossover trial [9]. Adults reporting elevated worry [10].
Sources
[9], [10]
Caveats
Two small trials. [9] tested a CBD and terpene formulation, not CBD alone, and used a consumer sleep tracker rather than a sleep lab.

Doses studied

The FDA-approved epilepsy trials used 10 or 20 mg/kg a day, split into two doses, for 14 weeks [1][2][3]. A healthy-adult safety trial used 5 mg/kg a day for 28 days [11]. Pain trials used 6 to 1,600 mg [7]. Sleep trials used 300 mg a day [9][10].

Risks

Reported risks6

ModerateVery common

Other adverse events in trials

Shown to raise diarrhea, vomiting, fatigue, sleepiness and loss of appetite in seizure trials, with 14% against 1% withdrawing for side effects.

The numbers and sources
How common
Very common: more than 1 in 10 people.
Effect
In the Lennox-Gastaut trial, adverse events occurred in 86% on CBD and 69% on placebo, and 14% vs 1% withdrew because of them [3]. Diarrhea, vomiting, fatigue, fever, somnolence and decreased appetite were more frequent with CBD [1][3].
Population
Patients with Dravet or Lennox-Gastaut syndrome [1][3]. Healthy adults [15].
Sources
[1], [3], [15]
Caveats
These patients took several other antiepileptic drugs. In 4 RCTs of 269 healthy adults, diarrhea was more likely on CBD than placebo (RR 5.85, 95% CI 1.14 to 30.02). Headache, abdominal pain, fatigue and dizziness did not differ significantly [15].
StrongCommon

Liver enzyme elevation

Shown to raise liver enzymes, about 6 times the odds on placebo, mostly at high doses or with antiepileptic drugs. No cases appeared under 300 mg a day in adults.

The numbers and sources
How common
Common: between 1 in 100 and 1 in 10 people.
Effect
Across 12 placebo-controlled trials (1,229 participants), CBD raised the odds of liver enzyme elevation (OR 5.85, 95% CI 3.84 to 8.92) and drug-induced liver injury (OR 4.82, 95% CI 2.46 to 9.45). In 28 trials, the pooled rate of enzyme elevation was 7.4% and of liver injury 3.0%. High dose (1,000 mg a day or more, or 20 mg/kg or more) and use with antiepileptic drugs were risk factors. No cases were reported in adults under 300 mg a day, and no severe injury was reported [12]. In an FDA-run trial of 201 healthy adults, 5 mg/kg a day for 28 days raised ALT or AST above 3 times normal in 5.6% on CBD and 0% on placebo, with increased eosinophilia [11]. In the Lennox-Gastaut trial, 9% of CBD patients had raised aminotransferases [2].
Population
Trial participants with epilepsy and healthy adults [2][11][12].
Sources
[2], [11], [12]
Caveats
In the healthy-adult trial, elevations meeting withdrawal criteria were found at day 21 in 2 people and day 28 in 5 [11]. Long-term effects at lower consumer doses were not measured [11].
ModerateHow often is not known

Drug interactions

Shown to raise clobazam levels by about 60% in children with epilepsy, and to change levels of several other antiepileptic drugs.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In 13 children taking clobazam, CBD raised clobazam levels by a mean 60% and its active metabolite by 500% at 4 weeks, and side effects in 10 of 13 eased when clobazam was reduced [13]. In 81 adults and children, rising CBD doses raised serum topiramate, rufinamide and N-desmethylclobazam and lowered clobazam. AST and ALT were higher in those also taking valproate [14].
Population
People with refractory epilepsy [13][14].
Sources
[13], [14]
Caveats
Open-label studies at prescription doses. Except for clobazam and its metabolite, the level changes stayed within accepted therapeutic ranges [14].
ModerateHow often is not known

Product content does not match the label

Most CBD products tested did not match their labels within 10%, and THC was found in 18 of 84 products bought online.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Of 84 CBD products bought online from 31 companies, 30.95% were labeled within 10% of measured CBD, 42.85% held more than labeled and 26.19% held less. THC was detected in 18 of 84, up to 6.43 mg/mL [16]. Of 516 US products, 42% fell within 10%, 40% held under 90% of the label, and lead was found in 42% of 121 edibles [17].
Population
Product testing [16][17].
Sources
[16], [17]
Caveats
Studies published in 2017 and 2022. Four edibles exceeded California's Proposition 65 daily lead threshold [17].
ModerateHow often is not known

Positive drug and anti-doping tests

WADA-prohibited cannabinoids CBG and CBDV appeared in most urine samples after 10 weeks of one CBD product. Positive THC tests traced mainly to undeclared THC and mislabeling.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
After 10 weeks of 150 mg a day of a broad-spectrum CBD product, the cannabinoids CBG and CBDV, which WADA prohibits, were found in 42% and 68% of urine samples before exercise and 74% and 84% after 90 minutes of exercise. THC and its metabolites were not detected [18]. A systematic review of 12 studies found that 5 of 8 human studies reported no THC result above test cut-offs after CBD or hemp oil use, though trace levels near detection limits occurred. Positive results traced mainly to undeclared or excess THC, mislabeling and contamination [19].
Population
36 healthy adults, 31 on CBD and 5 on placebo [18]. Human and analytical studies from 2014 to 2024 [19].
Sources
[18], [19]
Caveats
One product in [18]. Results depend on the product's content and the test's sensitivity [19].
ModerateHow often is not known

FDA position

FDA states it has not found adequate evidence on how much CBD can be consumed, and for how long, before causing harm, naming liver harm and drug interactions.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
On January 26, 2023, FDA said it was not apparent how CBD products could meet safety standards for dietary supplements or food additives, and that it had not found adequate evidence to determine how much CBD can be consumed, and for how long, before causing harm. It named potential harm to the liver, interactions with certain medications, possible harm to the male reproductive system, and concern for children and those who are pregnant [20].
Population
US consumers [20].
Sources
[20]
Caveats
The FDA-run 2025 trial found no change in testosterone, inhibin B or thyroid hormones after 28 days [11].

Claims tested and not found

  1. That CBD relieves pain. Fifteen of 16 randomized trials found no benefit over placebo [7].
  2. That CBD reduces nonconvulsive seizures in Dravet syndrome. The reduction in nonconvulsive seizures was not significant [1].
  3. That CBD eases sleep disturbance in people who worry. In 63 adults, 300 mg a day for 2 weeks did not differ significantly from placebo [10].
  4. That CBD lowers blood inflammation markers. Pooled IL-6, IL-8, IL-10 and TNF-α did not differ significantly from control [8].

Sources

  1. Devinsky O, Cross JH, Laux L, et al. Trial of Cannabidiol for Drug-Resistant Seizures in the Dravet Syndrome. New England Journal of Medicine. 2017. https://doi.org/10.1056/NEJMoa1611618
  2. Devinsky O, Patel AD, Cross JH, et al. Effect of Cannabidiol on Drop Seizures in the Lennox-Gastaut Syndrome. New England Journal of Medicine. 2018. https://doi.org/10.1056/NEJMoa1714631
  3. Thiele EA, Marsh ED, French JA, et al. Cannabidiol in patients with seizures associated with Lennox-Gastaut syndrome (GWPCARE4): a randomised, double-blind, placebo-controlled phase 3 trial. The Lancet. 2018. https://doi.org/10.1016/S0140-6736(18)30136-3
  4. Pratama R, Muhaimin M, Khairinisa MA, Chaerunisaa AY. Adjunctive Cannabidiol for Drug-Resistant Epilepsy: A Systematic Review and Meta-Analysis of Randomized Trials Across Syndromes, Formulations, and Dose Ranges. Therapeutics and Clinical Risk Management. 2026. https://doi.org/10.2147/tcrm.s601774
  5. de Oliveira HM, Oliveira Fonseca PE, Trejo Elías JE, et al. Cannabidiol Use in Developmental and Epileptic Encephalopathies: A Syndrome- and Age-Stratified Systematic Review and Meta-analysis. CNS Drugs. 2026. https://doi.org/10.1007/s40263-026-01301-z
  6. Han K, Wang JY, Wang PY, Peng YC. Therapeutic potential of cannabidiol (CBD) in anxiety disorders: A systematic review and meta-analysis. Psychiatry Research. 2024. https://doi.org/10.1016/j.psychres.2024.116049
  7. Moore A, Straube S, Fisher E, Eccleston C. Cannabidiol (CBD) Products for Pain: Ineffective, Expensive, and With Potential Harms. The Journal of Pain. 2024. https://doi.org/10.1016/j.jpain.2023.10.009
  8. Candeloro BM, de Oliveira CM, Gimenez FVM, et al. The Pleiotropic Influence of Cannabidiol and Tetrahydrocannabinol on Inflammatory Biomarkers: A Systematic Review and Meta-Analytical Synthesis. International Journal of Molecular Sciences. 2025. https://doi.org/10.3390/ijms262311618
  9. Wang M, Faust M, Abbott S, et al. Effects of a cannabidiol/terpene formulation on sleep in individuals with insomnia: a double-blind, placebo-controlled, randomized, crossover study. Journal of Clinical Sleep Medicine. 2025. https://doi.org/10.5664/jcsm.11324
  10. Gournay LR, Ferretti ML, Dickens HB, et al. The effects of cannabidiol on sleep disturbances within a sample of high trait worriers: A double-blind, randomized placebo controlled trial. Experimental and Clinical Psychopharmacology. 2026. https://doi.org/10.1037/pha0000832
  11. Florian J, Salcedo P, Burkhart K, et al. Cannabidiol and Liver Enzyme Level Elevations in Healthy Adults: A Randomized Clinical Trial. JAMA Internal Medicine. 2025. https://doi.org/10.1001/jamainternmed.2025.2366
  12. Lo LA, Christiansen A, Eadie L, et al. Cannabidiol-associated hepatotoxicity: A systematic review and meta-analysis. Journal of Internal Medicine. 2023. https://doi.org/10.1111/joim.13627
  13. Geffrey AL, Pollack SF, Bruno PL, Thiele EA. Drug-drug interaction between clobazam and cannabidiol in children with refractory epilepsy. Epilepsia. 2015. https://doi.org/10.1111/epi.13060
  14. Gaston TE, Bebin EM, Cutter GR, et al. Interactions between cannabidiol and commonly used antiepileptic drugs. Epilepsia. 2017. https://doi.org/10.1111/epi.13852
  15. Sawaira F, Shah MA, Hageen AW, et al. Safety of cannabidiol versus placebo in healthy population: a systematic review and meta-analysis. Annals of Medicine & Surgery. 2026. https://doi.org/10.1097/ms9.0000000000004549
  16. Bonn-Miller MO, Loflin MJE, Thomas BF, et al. Labeling Accuracy of Cannabidiol Extracts Sold Online. JAMA. 2017. https://doi.org/10.1001/jama.2017.11909
  17. Gardener H, Wallin C, Bowen J. Heavy metal and phthalate contamination and labeling integrity in a large sample of US commercially available cannabidiol (CBD) products. Science of the Total Environment. 2022. https://doi.org/10.1016/j.scitotenv.2022.158110
  18. Gillham SH, Cole PL, Owens DJ, et al. Daily Use of a Broad-Spectrum Cannabidiol Supplement Produces Detectable Concentrations of Cannabinoids in Urine Prohibited by the World Anti-Doping Agency: An Effect Amplified by Exercise. Medicine & Science in Sports & Exercise. 2026. https://doi.org/10.1249/mss.0000000000003842
  19. Ovat DY, Bezci E, Balıca K, et al. Impact of CBD and hemp oil use on drug test results: a systematic review. International Journal of Legal Medicine. 2026. https://doi.org/10.1007/s00414-026-03790-5
  20. US Food and Drug Administration. FDA Concludes that Existing Regulatory Frameworks for Foods and Supplements are Not Appropriate for Cannabidiol. 2023. https://www.fda.gov/news-events/press-announcements/fda-concludes-existing-regulatory-frameworks-foods-and-supplements-are-not-appropriate-cannabidiol

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