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Limited evidenceStress & mood

CBD (Cannabidiol)

CBD is a genuinely effective prescription anticonvulsant at 10-20 mg/kg/day — but the evidence for the reasons people actually buy it, anxiety, sleep and pain, is thin and inconsistent, and typical over-the-counter doses of 10-50 mg are far below anything ever shown to work. Product mislabelling is rampant.

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What the science says

  • Reduces seizures in Dravet and Lennox-Gastaut syndromes Strong evidence

    In a randomised, double-blind trial of 120 children and young adults with Dravet syndrome, CBD 20 mg/kg/day cut median monthly convulsive seizures from 12.4 to 5.9, versus 14.9 to 14.1 on placebo. Replicated trials led to regulatory approval of pharmaceutical CBD (Epidiolex/Epidyolex) — this is a prescription medicine at doses roughly 20-100 times what consumer products contain.

  • Reduces anxiety Limited evidence

    A systematic review of randomised trials in anxiety found a small, heterogeneous literature dominated by single-dose experimental studies using 300-600 mg CBD in laboratory-induced anxiety, such as simulated public speaking. Trials of repeated dosing in diagnosed anxiety disorders are few and results are inconsistent, and no trial supports the 10-25 mg doses typical of retail gummies and oils.

  • Improves sleep Limited evidence

    Sleep is usually a secondary outcome in CBD trials, and reviews of non-seizure indications find no consistent benefit for insomnia. Where sleep improves, it often tracks improvement in the primary condition such as pain or anxiety rather than a direct hypnotic effect.

  • Relieves chronic pain Limited evidence

    Systematic reviews of randomised trials of CBD alone for chronic pain report little consistent separation from placebo. Much of the positive cannabis pain literature involves THC-containing preparations, which is a different question entirely.

Dosage & safety

Studied dosePrescription CBD for epilepsy is titrated to 10-20 mg/kg/day in two divided doses. Experimental anxiety studies used single doses of 300-600 mg. Retail products typically supply 10-50 mg, a range with essentially no supporting efficacy data. CBD is fat-soluble and absorption increases several-fold when taken with a high-fat meal, which also means dosing on an empty stomach delivers substantially less.
SafetyDose-dependent adverse effects include somnolence, diarrhoea, decreased appetite, fatigue and elevated liver transaminases — the liver signal is real and much more common when combined with valproate. CBD inhibits CYP3A4 and CYP2C19 and raises levels of clobazam's active metabolite, warfarin and potentially many other drugs; check interactions before combining with any prescription medicine. Legal status varies by country and by product; some jurisdictions restrict or prohibit it. In sport, WADA has removed CBD from the prohibited list but all other cannabinoids including THC remain banned, and independent testing repeatedly finds retail CBD products mislabelled for CBD content and contaminated with THC — athletes have failed tests this way. Avoid in pregnancy and breastfeeding.

How to take it

TimingTake it in the evening if you are using it for sleep; otherwise timing does not matter as long as it is consistent.
With food?Take it with a high-fat meal - absorption increases several-fold compared with an empty stomach.
Worth knowingBe consistent about fed versus fasted dosing; that difference changes your actual exposure more than most dose adjustments people make.

Interactions

With medications

  • clobazam

    CBD raises levels of clobazam's active metabolite substantially, increasing sedation. do not combine without your neurologist adjusting the clobazam dose

  • valproate

    Liver transaminase elevations are markedly more common on the combination. do not combine without liver function monitoring

  • warfarin

    CBD inhibits CYP2C9 and raises INR. do not combine without INR monitoring arranged in advance

  • drugs metabolised by CYP3A4 or CYP2C19

    CBD inhibits both and can raise levels of a wide range of prescription drugs. check your full medication list with a pharmacist before starting

With other supplements

  • melatonin, valerian and other sedating supplements

    Additive somnolence and fatigue. add one at a time

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Does CBD work for anxiety?

The evidence for CBD in anxiety is limited: most studies used single 300-600 mg doses in laboratory-induced anxiety, and trials in diagnosed anxiety disorders are few and inconsistent. No trial supports the 10-25 mg doses in typical retail gummies and oils.

Does CBD help with sleep or chronic pain?

Reviews find no consistent benefit of CBD for insomnia, and trials of CBD alone for chronic pain show little separation from placebo. Where sleep improves, it often follows improvement in pain or anxiety rather than a direct effect.

Does CBD actually work for anything?

Yes, for seizures: strong evidence shows prescription CBD at 10-20 mg/kg/day reduces seizures in Dravet and Lennox-Gastaut syndromes, and in one trial cut median monthly seizures from 12.4 to 5.9. Those doses are roughly 20-100 times what consumer CBD products contain.

Does CBD interact with medications?

Yes: CBD inhibits CYP3A4 and CYP2C19, raises levels of clobazam's active metabolite and warfarin, and causes more liver enzyme elevations with valproate. Check your full medication list with a pharmacist before starting CBD.

Scientific references

Where to buy

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