Yes, CBD can interact with warfarin. Case reports describe INR (a measure of how long blood takes to clot) rising after CBD was started, and a systematic review rated warfarin among the potentially highest-risk CBD interactions.1 Anyone on a blood thinner should talk to their prescriber before starting, stopping or changing CBD.
How does the interaction work?
CBD slows several of the liver enzymes that clear medicines from the body, so blood levels of some medicines rise.2 CYP2C9 is one of the enzymes CBD affects, and the Australian product information for Epidyolex predicts an interaction with warfarin through that enzyme.23
What has been reported with warfarin?
| Finding | Detail |
|---|---|
| Case reports | INR rose after prescription CBD was started. In one, INR ranged up to 6.86 as CBD was increased, and the warfarin dose was cut by about 30%1 |
| Systematic review | Warfarin, valproate, tacrolimus and sirolimus rated as the potentially highest-risk interactions1 |
How sure are we? Moderate: case reports plus a plausible mechanism. Prescribers typically check INR more often when CBD is started, stopped or changed.1 A higher INR means a higher risk of bleeding.
What about clopidogrel?
Clopidogrel must be activated by the enzyme CYP2C19. CBD blocks that enzyme, so it may reduce the active form, which could make clopidogrel less effective.2 This is predicted from how the drugs work, not measured in people.
What about apixaban, rivaroxaban and other newer blood thinners?
Our research did not find verified studies of CBD with these medicines, so we cannot say what happens. An absence of studies is not proof of safety. A pharmacist can check your medicines against current interaction databases.
Do low doses interact?
Nobody has shown that low doses are free of interactions. Most measured interactions come from prescription doses of hundreds of milligrams or more. The UK Food Standards Agency has set a provisional upper limit of 10 mg of CBD a day for healthy adults, and advises people on prescription medication to avoid CBD foods without medical advice.4 For medicines with a narrow margin between a helpful and a harmful dose, such as warfarin, a small change in blood level can matter.2
Does stopping CBD matter too?
Yes. CBD lingers, with a half-life of 56 to 61 hours after regular dosing, so its effect on other medicines does not switch off the day it is stopped.2 Reviewers advise monitoring INR when stopping as well as starting.1
What should you do?
- Give your prescriber and pharmacist a full list of your medicines, including any CBD product, whatever its source.
- Report new bruising or bleeding promptly.
- Do not change your blood thinner dose yourself.
Read the full guide: CBD drug interactions.
Footnotes
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Nachnani R and others. Systematic review of drug-drug interactions of delta-9-tetrahydrocannabinol, cannabidiol, and Cannabis. Frontiers in Pharmacology, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC11167383/ ↩ ↩2 ↩3 ↩4 ↩5
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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
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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 ↩
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UK Food Standards Agency and Food Standards Scotland. Provisional cannabidiol (CBD) acceptable daily intake: lay summary, October 2023. https://www.gov.uk/government/publications/provisional-cannabidiol-cbd-acceptable-daily-intake-adi/lay-summary ↩
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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