CBD does cause side effects. The most common ones 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, and most of the numbers below come from people taking very large prescription doses with other medicines. 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 common are CBD side effects?
The best figures come from the placebo-controlled trials of Epidyolex, the purified CBD medicine registered for severe childhood epilepsies. The table shows how many people had each effect over up to 14 weeks.1
Read it with three things in mind. The average age of participants was 14. Everyone was also taking other anti-seizure medicines. And the doses, 10 and 20 mg per kg of body weight a day, equal roughly 700 and 1,400 mg a day for a 70 kg adult.1
| Side effect | CBD 10 mg/kg/day (75 people) | CBD 20 mg/kg/day (238 people) | Placebo (227 people) |
|---|---|---|---|
| Sleepiness (somnolence) | 23% | 25% | 8% |
| Decreased appetite | 16% | 22% | 5% |
| Diarrhoea | 9% | 20% | 9% |
| Raised liver enzymes | 8% | 16% | 3% |
| Fatigue, weakness or feeling unwell | 11% | 12% | 4% |
| Rash | 7% | 13% | 3% |
| Insomnia or poor sleep | 11% | 5% | 4% |
| Irritability or agitation | 9% | 5% | 2% |
| Infections (all types) | 41% | 40% | 31% |
We checked the column order of this table directly against the published label.1
In the same trials, 2.7% of people on the lower dose and 11.8% on the higher dose stopped treatment because of a side effect, compared with 1.3% on placebo. The most frequent reason was raised liver enzymes.1
A separate trial in tuberous sclerosis complex used 25 mg per kg a day. There, diarrhoea affected 31% on CBD and 25% on placebo, raised liver enzymes 25% and 0%, decreased appetite 20% and 12%, vomiting 17% and 9%, and fever 19% and 8%.1
Are side effects the same at lower doses?
They appear to be fewer, but the data are thinner.
A 2020 meta-analysis pooled randomised trials of CBD across many conditions. CBD was linked to more diarrhoea (odds ratio 2.61) and sleepiness (odds ratio 2.23) than placebo. When the childhood epilepsy trials were removed, the only side effect still linked to CBD was diarrhoea. The authors’ explanation is that many effects in epilepsy trials reflect interactions with other anti-seizure medicines.3
A review of oral CBD trials published from 2020 to 2022 found most side effects were mild or moderate. The most frequent were stomach and bowel complaints (59.5% of reported events), sleepiness (16.7%), loss of appetite (16.5%) and raised liver enzymes (12.8%).4
A University of Sydney review of oral doses up to 400 mg a day found that raising the dose from 60 to 400 mg a day did not appear to increase side effects.5 In an Australian insomnia trial, 150 mg of CBD each night for two weeks did not impair thinking the next day, though dry mouth was more common than with placebo.6
Liver enzyme rises are the exception. They have been seen in healthy adults at around 350 to 400 mg a day. See CBD and the liver.
Why does CBD make some people sleepy?
Sleepiness is the best-documented nervous system effect. Across the epilepsy trials, sleepiness or sedation (including lethargy) affected 32% of people on CBD and 11% on placebo.1
Much of that came from one interaction. Among people also taking the anti-seizure medicine clobazam, 46% had sleepiness or sedation. Among those not taking clobazam, it was 16%.1 CBD roughly triples blood levels of clobazam’s active breakdown product, which is itself sedating.1 Alcohol and other sedating medicines can add to the effect.1
The label notes that sleepiness is more common early in treatment and may ease with time.1 Until you know how CBD affects you, treat it like any medicine that can cause drowsiness. See CBD and driving.
What about appetite and weight?
High-dose CBD lowers appetite, and some people lose weight. In the epilepsy trials, 16% of people on CBD lost at least 5% of their body weight, compared with 8% on placebo. The effect grew with dose: 18% at 20 mg per kg a day and 9% at 10 mg per kg a day.1 In growing children this is watched closely. The Australian product information says ongoing weight loss, or a lack of weight gain, should be checked from time to time.7
Less common effects that prescribers watch for
These come from prescription-dose data, mostly in epilepsy.
- Blood changes. Small falls in haemoglobin (the oxygen-carrying protein in red blood cells) were seen, and the TGA’s assessment of Epidyolex noted anaemia in trials.18
- Allergic reactions. Some trial participants had itching, skin redness or swelling that needed treatment. Epidyolex contains sesame oil, so it is not used in people with a sesame allergy.17
- Pneumonia. This was seen more often in people taking CBD together with clobazam (10% to 17%, against 1% on placebo with clobazam).1
- Mood changes. All anti-seizure medicines, CBD included, carry a warning about a small increase in suicidal thoughts. The label estimates about one extra case for every 530 people treated with anti-seizure medicines generally.1
- Kidney blood test. Creatinine, a marker used to check kidney function, rose about 10% within two weeks. A follow-up study in healthy adults suggested this was not due to reduced kidney filtering.1
What does the TGA say?
The TGA’s patient information on medicinal cannabis lists the known side effects of both CBD and THC as fatigue and sedation, vertigo, nausea and vomiting, fever, decreased or increased appetite, dry mouth and diarrhoea. It says CBD-rich products generally cause fewer side effects than high-THC products, but that the CBD doses needed in conditions such as childhood epilepsy can be high enough that a proportion of patients get side effects.9
That guidance is dated December 2017 and covers medicinal cannabis in general, so parts of it are written with THC in mind.9
Is it CBD, or something else in the bottle?
Feeling “high”, anxious, confused or having a racing heart is not typical of pure CBD. In a human abuse-potential study, single doses up to 4,500 mg did not produce THC-like effects.1 If these happen, the product may contain THC. In one United States study of 84 CBD products bought online, only 31% were accurately labelled.10 See Is what is on the label in the bottle?.
When to get medical help
Contact your prescriber or pharmacist if a side effect is troubling or does not settle. They decide whether a dose or medicine should change.
Seek medical advice promptly for signs that can point to a liver problem: unexplained nausea or vomiting, pain in the upper right of the abdomen, unusual tiredness, loss of appetite, yellowing of the 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, at any time.11 Call 000 in an emergency.
Suspected side effects of any medicine can be reported to the TGA.12
What we do not know
Most safety data cover weeks to a few months. The populations studied are mainly children and young adults with epilepsy on several medicines, or small groups of healthy volunteers. There are no large, long-term controlled studies of low daily doses in older adults, pregnant women or people with chronic illness. Those groups are covered in Who should not take CBD?.
Footnotes
-
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 ↩7 ↩8 ↩9 ↩10 ↩11 ↩12 ↩13 ↩14 ↩15 ↩16 ↩17 ↩18 ↩19
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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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Review of adverse events in randomised trials of oral cannabidiol published 2020 to 2022. https://pmc.ncbi.nlm.nih.gov/articles/PMC9782576/ ↩
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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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Next-day cognition results from the Australian trial of 150 mg nightly CBD in insomnia, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC11063694/ ↩
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Therapeutic Goods Administration. Epidyolex (cannabidiol) Australian Product Information, version attached to the AusPAR, January 2021 (may be superseded). https://www.tga.gov.au/sites/default/files/auspar-cannabidiol-210115-pi.pdf ↩ ↩2
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Therapeutic Goods Administration. Australian Public Assessment Report for cannabidiol (Epidyolex), January 2021. https://www.tga.gov.au/sites/default/files/auspar-cannabidiol-210115.pdf ↩
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Therapeutic Goods Administration. Guidance for the use of medicinal cannabis in Australia: patient information, version 1, December 2017. https://www.tga.gov.au/sites/default/files/guidance-use-medicinal-cannabis-australia-patient-information.pdf ↩ ↩2
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Bonn-Miller and others. Labelling accuracy of 84 cannabidiol products sold online. JAMA, 2017. https://jamanetwork.com/journals/jama/fullarticle/2661569 ↩
-
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 ↩
Common questions
Does CBD make you sleepy?
It can. In the epilepsy trials, sleepiness or sedation affected 32% of people on CBD and 11% on placebo, and it was much more common in people also taking clobazam. A small Australian trial of 150 mg nightly found no next-day impairment in thinking. Sleepiness is more likely at high doses and with alcohol or other sedating medicines.
Can CBD cause diarrhoea or an upset stomach?
Yes. Diarrhoea is the side effect most consistently linked to CBD across trials. At 20 mg per kg a day it affected 20% of people compared with 9% on placebo. Some people also report nausea, and lower appetite is common at high doses.
What are the long-term side effects of CBD?
Nobody knows for certain. The longest controlled data come from people with severe epilepsy on high prescription doses, where weight loss and liver enzyme rises needed ongoing monitoring. There are no good long-term controlled studies of small daily doses in otherwise healthy adults.
How do I report a side effect from CBD?
Tell your prescriber or pharmacist first. Anyone in Australia can also report a suspected side effect of a medicine to the Therapeutic Goods Administration through its reporting-problems web page. For urgent advice about a possible poisoning, call the Poisons Information Centre on 13 11 26.
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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