CBD–Medication Interactions: Specific Examples and Mechanisms

Read this first

This page is education only. It does not tell anyone to start, stop, skip or change any medicine. If you take prescription medicines and use, or are thinking about using, any CBD product, tell the prescriber or a pharmacist. See talking with a health professional. For a general overview, see cannabis and CBD: medicine interactions and toxicology. If someone has taken too much of anything, call US Poison Help at 1-800-222-1222, or 911 for severe symptoms. [1]

Evidence labels and an important limit

Approved-drug label means the statement comes from the US prescribing information for Epidiolex, the FDA-approved purified CBD medicine, as read from DailyMed (version dated 2026-05-29). Those statements describe that medicine at the amounts used in its patients, mainly children and adults with certain severe epilepsies. They are not a measure of what happens with over-the-counter oils or gummies, whose content varies. The FDA says unapproved CBD products have not been evaluated for how they could interact with other drugs or foods. [2] Other labels: systematic review, case reports, preclinical (cells, animals or computer models only), insufficient evidence.

Why interactions happen

Many medicines are cleared by liver enzymes called cytochrome P450 (CYP) enzymes, and by carrier proteins such as P-glycoprotein. A 2023 review reported that CBD inhibits several of them, including CYP3A4/5, CYP2C9, CYP2C19, CYP2B6, CYP2D6, CYP1A2, UGT1A9 and P-glycoprotein. [3] The label says CBD itself is processed mainly by CYP2C19 and CYP3A4, and UGT enzymes. [4] THC is processed by many of the same enzymes (CYP3A4, CYP2C9, CYP2C19). [5]

A 2023 review identified 403 drugs handled by these proteins and found CBD interactions reported for 53 of them in humans, animals or lab studies. In 31 of the 53, CBD increased the level of the other drug. Interactions in people were reported for 25. The authors said the relevance is largely unknown and that pharmacologic studies are urgently needed. [3]

What the Epidiolex label documents

The label tells prescribers to consider dose changes in some cases. Those are decisions for the prescriber and the patient together.

Clobazam in more detail

A 2020 trial simulation found that the seizure benefit of CBD in Lennox-Gastaut syndrome may be partly explained by the clobazam interaction. [6] A 2019 study in cells and mice found CBD blocked the enzymes that break down clobazam and its metabolite, and also enhanced GABA-A receptor activity together with clobazam. [7] Label: preclinical. Approved-drug seizure outcomes are covered in approved cannabinoid medicines.

Valproate in more detail

A 2023 computer-model study could not reproduce the higher liver-enzyme rate seen with valproate through the three liver-injury mechanisms it modeled, so the cause of the label's finding is not settled. [8] Label: preclinical (model).

Warfarin

A 2023 systematic review of anticoagulant interactions found that, apart from warfarin, evidence for an interaction with anticoagulants is non-existent. For warfarin there were seven case reports, with INR (a blood-clotting measure) raised in six of seven; the amounts were either very high (for example more than 600 mg a day of CBD) or unknown. The authors rated the data very low quality but supportive of a potential interaction. [9] Label: insufficient evidence, a recognized signal. A 2024 systematic review of narrow-therapeutic-index medicines found warfarin, valproate, tacrolimus and sirolimus among the interactions most widely reported for cannabinoids. [5]

Liver

The label describes dose-related transaminase elevations and tells prescribers to measure liver tests before and during treatment. [4] In a small trial, 16 healthy adults took 1,500 mg a day for about 3.5 weeks (a study amount); 44% had ALT above normal and 31% exceeded five times the upper limit. [10] See liver-related considerations for cannabinoids.

What is not known

The FDA says research on CBD with herbs and other plant products is limited. [2] The label says insufficient data exist to assess the risk of using other liver-toxic drugs with Epidiolex. [4] Most over-the-counter combinations have not been studied. For background on how interactions work, see how interactions work and interactions by drug class.