Last updated: October 2026
CBD is generally well tolerated. The most common side effects are tiredness, diarrhoea, nausea, dry mouth and changes in appetite, mostly at high doses. You can’t fatally overdose on CBD, but very high doses can raise liver enzymes, and CBD interacts with some medicines. The FSA advises healthy adults to take no more than 10mg a day as a precaution.
Below: common and rarer side effects, what happens if you take too much, the liver question, who should avoid CBD, and how to cut your risk.
Common side effects
| Side effect | How common | What helps |
|---|---|---|
| Tiredness or drowsiness | Common, especially at higher doses | Take it in the evening; lower the dose |
| Diarrhoea or loose stools | Common at high doses | Lower the dose; take with food; try capsules |
| Nausea | Occasional | Take with food |
| Dry mouth | Occasional | Drink water |
| Appetite changes | Reduced appetite is common at prescription doses | Usually settles with a lower dose |
| Headache | Occasional | Lower the dose |
In a trial in healthy volunteers, single doses up to 6,000mg were generally well tolerated, with diarrhoea, nausea, headache and sleepiness the most common effects. Those doses are hundreds of times higher than a supplement.
Can you overdose on CBD?
Not in the sense of a dangerous or fatal overdose: no deaths have been linked to CBD alone, and it doesn’t slow breathing the way opioids do. But “too much” is still possible, causing unpleasant side effects. If someone has taken a large amount of a product that might contain THC, especially a child, call 111 for advice, or 999 if they’re very drowsy, confused or struggling to breathe.
What happens if you take too much?
- Strong drowsiness and feeling “heavy”
- Diarrhoea, nausea or an upset stomach
- Light-headedness, as CBD can lower blood pressure slightly at high doses. See CBD and heart palpitations
These usually wear off within hours. Rest, drink water, don’t drive, and take less next time. If you feel high or anxious, the product may have contained THC. See does CBD get you high?
CBD and the liver
At high doses, CBD can raise liver enzymes. In a 2021 study of 16 healthy adults taking 1,500mg a day, 7 had raised liver enzymes, and in 5 they rose above five times the normal limit. Liver changes are also listed for prescription CBD, especially alongside the epilepsy medicine valproate. Concerns about long-term effects on the liver and thyroid are part of why the FSA set its precautionary 10mg a day figure. See CBD and liver enzymes and the 10mg guidance explained.
The FSA’s 10mg a day figure is precautionary advice rather than a legal limit, set while longer-term safety research continues. At Evopure we think it is a very cautious figure, and many adults use more. If you go above it, increase slowly, and check with your GP or pharmacist first if you take any medication.
Medicine interactions
CBD slows liver enzymes that break down many medicines, including some blood thinners, epilepsy, transplant, heart and sedative medicines. If your medicine has a grapefruit warning, check with a pharmacist before using CBD. Full guide: can CBD interact with medication?
Who should avoid CBD
- People who are pregnant, breastfeeding or trying to conceive (FSA advice)
- Under-18s
- People with liver disease, unless their doctor agrees
- People taking medicines that interact, unless a pharmacist or doctor agrees
- Anyone who needs to pass drug tests, unless the product has no detectable THC
How to reduce side effects
- Start low, around 10mg a day, and increase slowly.
- Take it with food to ease stomach effects.
- Try the evening if it makes you sleepy.
- Choose THC-free, lab-tested CBD. See how to read a lab report.
- Don’t combine with alcohol or other sedatives. See CBD and alcohol.
See also how much CBD to take.
FAQs
What are the side effects of CBD?
Most commonly tiredness, diarrhoea, nausea, dry mouth and appetite changes, mainly at high doses. High doses can also raise liver enzymes.
Can you overdose on CBD?
Not fatally. No deaths have been linked to CBD alone, but taking too much can cause drowsiness, diarrhoea and nausea.
What happens if you take too much CBD?
You may feel very sleepy, light-headed or sick, or get diarrhoea. Rest, drink water, don’t drive, and take less next time.
Is CBD bad for your liver?
At high doses it can raise liver enzymes. At supplement doses the risk appears much lower, but avoid CBD if you have liver disease unless your doctor agrees.
How long do CBD side effects last?
Usually a few hours. If side effects persist, stop taking it and speak to a pharmacist or GP.
Can CBD make you feel worse?
Some people feel tired, sick or unsettled, especially at higher doses or with products containing THC. Lowering the dose usually helps.
Sources
- Taylor L et al. A phase I, randomized, double-blind, placebo-controlled, single ascending dose, multiple dose, and food effect trial of the safety, tolerability and pharmacokinetics of highly purified cannabidiol in healthy subjects. CNS Drugs, 2018.
- Watkins PB et al. Cannabidiol and abnormal liver chemistries in healthy adults. Clin Pharmacol Ther, 2021.
- emc. Epidyolex: summary of product characteristics.
- GOV.UK. FSA consumer advice on CBD.
