Last updated 9 August 2026 · Originally published 16 May 2020
This is the CBD question with the clearest practical stakes. Not whether it works — whether it will interfere with something you already take.
The short answer: CBD can interact with medication, several important interactions are well established, and a pharmacist can usually check your particular combination in a few minutes.
The grapefruit warning is a useful clue — not a complete test
Look at your medication’s label or leaflet. If it says avoid grapefruit, that’s a good reason to check with a pharmacist before taking CBD.
Grapefruit and CBD can both affect enzymes involved in processing medicines, but they don’t behave identically. A grapefruit warning doesn’t prove CBD will interact with that drug, and the absence of one doesn’t prove the combination is safe — CBD affects several enzymes and transport proteins that grapefruit doesn’t.
Treat it as a flag to investigate rather than a yes-or-no test.
Why it happens
Your body clears medicines using a set of enzymes and transport proteins. CBD can interfere with several of them — particularly CYP2C19, but also CYP1A2, CYP2C8, UGT1A9 and a transporter called P-glycoprotein. Which one matters depends on the medication.
CBD can raise levels of some drugs. If it slows the pathway that clears your medication, more of it stays in your bloodstream. The dose you were prescribed effectively becomes a larger one.
It can also reduce the effect of a drug that needs activating. Clopidogrel, an antiplatelet medicine, is swallowed as an inactive prodrug — it has to be converted into its working form, partly via CYP2C19. Inhibit that enzyme and you may get less active drug, not more.
Other medicines can alter CBD levels. Strong enzyme inducers such as rifampicin can lower CBD exposure substantially. Interestingly, and contrary to what was once expected, clinical studies have found that strong CYP3A4 and CYP2C19 inhibitors produce only small changes in CBD exposure.
Which medications deserve particular attention
Not an exhaustive list — and interaction risk depends on the specific drug rather than simply the category it belongs to.
Clobazam. One of the clearest interactions there is. Prescription CBD substantially raises levels of clobazam’s active metabolite, which is why drowsiness is so much more common in patients taking both.
Valproate. Combining it with prescription CBD increases the risk of elevated liver enzymes, even though CBD doesn’t appear to increase valproate concentrations.
Transplant and immunosuppressant drugs. CBD can substantially increase exposure to everolimus, and may raise tacrolimus and sirolimus levels. These need close monitoring because small changes matter a great deal.
Warfarin. Case reports describe rising INR and warfarin doses needing reduction after CBD was introduced. Anyone on warfarin should have the combination checked, and may need extra INR monitoring.
Citalopram. The evidence here strengthened considerably in 2026. A clinical study found repeated CBD increased total citalopram exposure by around 43% — comparable to the effect of known CYP2C19 inhibitors.[1] Participants took 5 mg of CBD per kilogram of body weight daily, which is 350 mg a day for a 70 kg adult: below common prescription epilepsy doses, but far above a typical gummy. Citalopram labelling already specifies a lower maximum dose alongside CYP2C19 inhibitors. Escitalopram is closely related and shares some of the same metabolic pathways, but it wasn’t tested in this study.
Clopidogrel. CBD may reduce its activation and therefore its antiplatelet effect. Pharmacologically credible; direct clinical evidence still limited.
Sedatives. CBD can add to drowsiness from benzodiazepines, opioids, alcohol and other depressants — even where no important metabolic interaction has been shown.
Other drugs may interact through different enzymes or transporters entirely. That’s why checking your specific medication is more useful than scanning a list of drug classes.
Two things people get wrong
Spacing the doses usually isn’t a reliable fix. You’ll see advice to take CBD and your medication a couple of hours apart. For this kind of interaction that generally doesn’t work — enzyme inhibition can persist well beyond a few hours, and it isn’t about the two substances meeting in your stomach.
Topicals are a different case. Creams and balms are intended to act locally and little tends to reach the bloodstream, so the interaction concern is much smaller. Transdermal patches are designed to get cannabinoids into circulation, so treat them like anything you swallow.
How worried should you be?
It depends heavily on dose, and this is where a lot of alarming coverage loses the thread.
Much of the strongest evidence comes from prescription CBD at 10 to 25 mg per kilogram of body weight daily — hundreds of milligrams, sometimes more. A 15 mg gummy is a very different exposure.
But the 2026 citalopram study cautions against assuming interactions only happen at the highest prescription doses: it found a measurable one at 5 mg/kg daily.[1] That still amounts to hundreds of milligrams for most adults. There’s much less clinical evidence at ordinary retail doses, so a 15 mg gummy shouldn’t be treated as equivalent — but nor can low doses be declared interaction-free.
And where a drug has a narrow therapeutic window — warfarin, immunosuppressants, some anti-epileptics — a modest shift matters more than it would elsewhere.
What to actually do
Check for the grapefruit warning on everything you take.
Talk to a pharmacist. They can run your specific medications against interaction data in a few minutes, and you don’t need an appointment. This is the single most useful step here.
Don’t stop prescribed medication to make room for CBD.
If you take something that requires monitoring — INR checks on warfarin, drug levels for immunosuppressants — tell whoever does the monitoring that you’ve started CBD.
If you take warfarin, clopidogrel, an immunosuppressant, an anti-seizure medicine or anything else requiring blood tests or careful dose control, check before starting CBD rather than relying on a low starting dose.
None of this is medical advice, and none of it should replace a conversation with a doctor or pharmacist who knows what you’re taking.
For more, see does CBD cause liver damage?, our guide to CBD and what the research actually shows, or browse Health Conditions.
References
- Salcedo P, Volpe DA, Chaturbedi A, Shah A, Florian J, et al. Clinical study to evaluate drug interactions of cannabidiol with citalopram and morphine in healthy adults. Clinical Pharmacology & Therapeutics. 2026;119(4):1095–1104. doi:10.1002/cpt.70219
- Balachandran P, ElSohly M, Hill KP. Cannabidiol interactions with medications, illicit substances, and alcohol: a comprehensive review. Journal of General Internal Medicine. 2021;36(7):2074–2084. doi:10.1007/s11606-020-06504-8
- Jiang R, Yamaori S, Takeda S, Yamamoto I, Watanabe K. Identification of cytochrome P450 enzymes responsible for metabolism of cannabidiol by human liver microsomes. Life Sciences. 2011;89(5–6):165–170. doi:10.1016/j.lfs.2011.05.018
- Jiang R, Yamaori S, Okamoto Y, Yamamoto I, Watanabe K. Cannabidiol is a potent inhibitor of the catalytic activity of cytochrome P450 2C19. Drug Metabolism and Pharmacokinetics. 2013;28(4):332–338. doi:10.2133/dmpk.dmpk-12-rg-129
- Iffland K, Grotenhermen F. An update on safety and side effects of cannabidiol: a review of clinical data and relevant animal studies. Cannabis and Cannabinoid Research. 2017;2(1):139–154. doi:10.1089/can.2016.0034
- Epidiolex (cannabidiol) oral solution: US prescribing information. DailyMed
About this article
Substantially rewritten in August 2026, combining our earlier reporting on CBD’s effect on liver enzymes and its interactions with medication. This update adds the grapefruit-warning check and identifies the medications with the clearest documented risks. It also incorporates the 2026 clinical study of CBD and citalopram, and corrects the widespread suggestion that spacing doses avoids an interaction. With earlier reporting by Sabina Pulone.
