Last updated: October 2026
CBD isn’t known to cause constipation. In trials of prescription CBD, the common gut side effect was the opposite: diarrhoea, in up to about a fifth of people at high doses. Constipation is listed among side effects of THC-containing products and many other medicines, so check other causes first.
Below: what the research shows, other likely causes, what to do, and when to see a GP.
What the research shows
| Side effect | In prescription CBD (Epidyolex) trials |
|---|---|
| Diarrhoea | Very common and dose-related: 13% at 10mg per kg a day and 21% at 20mg per kg, versus 10% on placebo |
| Nausea and vomiting | Common |
| Constipation | Not listed as a common side effect |
Those doses are far higher than food supplements. At typical supplement amounts, gut side effects are uncommon. See CBD side effects.
Other likely causes
- THC in the product: cannabis containing THC can slow the gut. Choose broad spectrum or isolate with a batch lab report.
- Other medicines: opioid painkillers, some antidepressants, iron tablets and some antacids commonly cause constipation.
- Diet and fluids: not enough fibre or water.
- Less movement: being less active, or travelling.
- Other ingredients: some capsules contain fillers; our CBD capsules contain inulin, a fibre that some people find changes their bowel habits at first.
What helps
| Step | Detail |
|---|---|
| Fibre | Increase gradually: fruit, vegetables, oats, wholegrains, beans |
| Fluids | Drink plenty of water through the day |
| Movement | A daily walk helps keep things moving |
| Routine | Don’t ignore the urge; give yourself time |
| Pharmacy laxatives | Short term, if lifestyle changes aren’t enough |
| Magnesium | Citrate has a gentle laxative effect. See magnesium for constipation |
See also supplements for digestion and magnesium for bloating.
When to see a GP
See a GP if constipation lasts more than a few weeks, keeps coming back, or comes with blood in your stools, unexplained weight loss, severe tummy pain, or a lasting change in bowel habit, especially if you’re over 50. Don’t stop prescribed medicines without advice.
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. We don’t recommend our products during pregnancy or breastfeeding.
FAQs
Can CBD oil cause constipation?
It isn’t a known side effect. Trials of prescription CBD found diarrhoea, not constipation, at high doses.
Does CBD cause diarrhoea?
It can, mainly at high doses. In prescription CBD trials, up to about a fifth of people had diarrhoea at the higher dose.
Why am I constipated after starting CBD?
Look at other causes first: THC in the product, other medicines, diet, fluids and activity. If it persists, see a GP.
Can CBD help constipation?
There’s no evidence it does. Fibre, fluids, activity and, if needed, laxatives or magnesium citrate are better options.
Sources
- Electronic Medicines Compendium. Epidyolex: summary of product characteristics (section 4.8, side effects).
- NHS. Constipation.
