Cannabis and CBD Drug Interactions: What Is Known

This page explains what published research and the FDA say about interactions. It is not a list of safe or unsafe combinations, and it is not a substitute for a pharmacist or prescriber who knows your medicines. Don't stop, start, or change a prescribed medicine on your own because of anything here. The FDA notes that consumer use of CBD products should always be discussed with a healthcare provider.

There are two broad kinds of interaction.

Pharmacokinetic (how the body processes a drug). THC and CBD are largely metabolized in the liver by cytochrome P450 (CYP) enzymes. A 2023 clinical review in Deutsches Ärzteblatt reports that strong CYP3A4 inhibitors such as verapamil and clarithromycin can raise THC levels, and strong inducers such as rifampicin and carbamazepine can lower them. In the other direction, THC and CBD inhibit CYP2C and CYP3A4, which can raise levels of other drugs those enzymes clear. A 2025 review in Pharmaceutics compiles the evidence for these enzyme-level interactions between cannabis products and prescription drugs.

Pharmacodynamic (drugs with overlapping effects). The FDA warns that using CBD with alcohol or other drugs that slow brain activity, such as those used for anxiety, panic, stress, or sleep problems, increases the risk of sedation and drowsiness, which can lead to injuries. The CDC notes that cannabis and alcohol together can increase impairment behind the wheel.

• Clobazam (an epilepsy medicine). In 13 children taking clobazam alongside CBD in an expanded-access program, levels of clobazam's active metabolite rose by a mean of about 500% at 4 weeks. Side effects were reported in 10 of the 13 and eased when doctors reduced the clobazam dose; the authors said monitoring levels is necessary when the two are combined.
• Warfarin (a blood thinner). A published case report describes a patient on warfarin whose INR (a measure of blood clotting time) rose after starting prescription CBD. The authors proposed CBD's inhibition of CYP2C9 and CYP3A4 as the mechanism and suggested INR monitoring when cannabinoids are started or increased.
• Liver effects. During its review of the prescription CBD drug Epidiolex, the FDA identified a risk of liver injury that was increased when taken with other drugs that affect the liver, though signs of liver injury also appeared in patients not on those drugs.

The Deutsches Ärzteblatt review concludes that potential interactions are probably of little importance at low or moderate doses, with clinically relevant enzyme interactions more likely at higher daily amounts, and that inhaled use can worsen interactions. That is a statement about averages in a clinical population, not a safe threshold for you. The FDA also notes there is limited research on CBD with herbs and dietary supplements and urges caution there too.

Product labels add uncertainty: the FDA has found many CBD products did not contain the amount of CBD they claimed, so the dose you think you are taking may not be the dose you get.

• Tell your pharmacist and prescriber about any cannabis or CBD use, including gummies, oils, and topicals, the same way you would list a supplement.
• Ask specifically about medicines with narrow safety margins or sedating effects, the categories behind the documented cases above.
• Avoid combining cannabis or CBD with alcohol or other sedating substances before driving or other tasks that need full attention.
• If you have symptoms after combining products, call poison control at 1-800-222-1222 or 911 in an emergency, as the CDC advises.