The most common side effects of CBD in clinical trials are sleepiness, reduced appetite and diarrhoea, and at high doses blood tests often show raised liver enzymes.1 They are dose-related. The World Health Organization describes CBD as “generally well tolerated with a good safety profile”, while noting that some reported effects may come from interactions with other medicines.2
How often did side effects happen in trials?
These figures are from placebo-controlled trials of Epidyolex in severe childhood epilepsy. Participants averaged 14 years old, all took other anti-seizure medicines, and the doses equal roughly 700 and 1,400 mg a day for a 70 kg adult.1
| Side effect | CBD 10 mg/kg/day | CBD 20 mg/kg/day | Placebo |
|---|---|---|---|
| Sleepiness | 23% | 25% | 8% |
| Decreased appetite | 16% | 22% | 5% |
| Diarrhoea | 9% | 20% | 9% |
| Raised liver enzymes | 8% | 16% | 3% |
| Fatigue or feeling unwell | 11% | 12% | 4% |
| Rash | 7% | 13% | 3% |
Source: US prescribing information.1
Are side effects the same at lower doses?
They appear to be fewer, but the data are thinner. A 2020 analysis of randomised trials across many conditions linked CBD to more diarrhoea and sleepiness than placebo. With the childhood epilepsy trials removed, the only side effect still linked to CBD was diarrhoea.3 An Australian review of oral doses up to 400 mg a day found side effects did not appear to increase between 60 and 400 mg.4
Liver enzyme rises are the exception. They have been seen in healthy adults at around 350 to 400 mg a day.5 See is CBD bad for your liver?
Why does CBD make some people sleepy?
Partly through interactions. In epilepsy trials, sleepiness or sedation affected 46% of people also taking clobazam, against 16% of those not taking it. Alcohol and other sedating medicines can add to the effect.1 Until you know how CBD affects you, treat it like any medicine that can cause drowsiness. See can you drive on CBD oil?
What if I feel high or anxious?
That is not typical of pure CBD. Single doses up to 4,500 mg did not produce THC-like effects in a human study.1 If it happens, the product may contain THC.
When should you get help?
Contact your prescriber or pharmacist if a side effect is troubling. Seek advice promptly for possible liver signs: unexplained nausea or vomiting, pain in the upper right of the abdomen, unusual tiredness, yellow skin or eyes, or dark urine.1 For a suspected overdose or a child who has swallowed a cannabis product, call the Poisons Information Centre on 13 11 26.6 Suspected side effects can be reported to the TGA.7
Most safety data cover weeks to months. “Few known problems” is not the same as “proven safe”.
Read the full guide: CBD side effects.
Footnotes
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Jazz Pharmaceuticals. Epidiolex (cannabidiol) oral solution, US prescribing information, DailyMed (accessed November 2026). https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=8bf27097-4870-43fb-94f0-f3d0871d1eec ↩ ↩2 ↩3 ↩4 ↩5 ↩6
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World Health Organization Expert Committee on Drug Dependence. Cannabidiol (CBD) critical review report, 2018. https://cdn.who.int/media/docs/default-source/controlled-substances/whocbdreportmay2018-2.pdf ↩
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Chesney E and others. Systematic review and meta-analysis of the adverse effects of cannabidiol in randomised trials, 2020. https://pubmed.ncbi.nlm.nih.gov/32268347/ ↩
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Arnold JC, McCartney D, Suraev A, McGregor IS. Review of the safety and efficacy of low oral doses of cannabidiol. Clinical and Translational Science, 2023. https://pubmed.ncbi.nlm.nih.gov/36259271/ ↩
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JAMA Network. News release on Florian J and others, cannabidiol and liver enzyme level elevations in healthy adults, JAMA Internal Medicine, 7 July 2025. https://www.eurekalert.org/news-releases/1089832 ↩
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healthdirect. Poisoning (Poisons Information Line 13 11 26). https://www.healthdirect.gov.au/poisoning ↩
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Therapeutic Goods Administration. Reporting problems. https://www.tga.gov.au/reporting-problems ↩
This page is general information, not medical or legal advice. Laws and evidence change; we show the date we last checked the facts at the top of every page. Talk to your doctor or pharmacist before starting, stopping or changing any medicine.
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