Cannabis and Medication Interactions to Discuss Before Your Visit

If you take a blood thinner, a sleep aid or a handful of daily pills, you may wonder how cannabis would fit in. The answer depends on what you take, how much, and how your body handles it. This guide explains why interactions matter and what to tell your clinician so the decision is a safe one.

Why Interactions Matter

An interaction happens when one substance changes how another works in your body. It can make a medicine stronger, weaker or less predictable, or it can stack side effects on top of each other. The National Center for Complementary and Integrative Health (NCCIH) notes that CBD use has been associated with liver injury and with interactions with other drugs.

Cannabis products may contain THC, CBD or both, and each can matter. Research on many specific combinations is limited, so the honest answer is often "we don't know for sure." That is exactly why your clinician wants the full picture before making a decision.

Three Ways Cannabis May Interact

Extra drowsiness. The FDA warns that using CBD with alcohol or other drugs that slow brain activity increases the risk of sedation and drowsiness, which can lead to injuries. The prescribing label for Epidiolex, the FDA-approved CBD medicine, gives a similar warning about other central nervous system depressants, including alcohol.

Liver enzyme effects. Your liver breaks down many medicines using enzymes. CBD is processed by some of the same enzymes and may change how quickly other drugs are cleared. The Epidiolex label describes interactions with drugs that affect the enzymes CYP3A4 and CYP2C19, and with the seizure medicine clobazam. It also warns that CBD can raise liver enzyme levels, and that the risk is higher with valproate. A 2019 review in the Journal of Clinical Medicine points out that these enzyme families help process a large share of common medicines.

Bleeding risk with blood thinners. A 2023 systematic review found case reports in which people taking warfarin had higher INR results, a measure of how long blood takes to clot, after using THC or CBD. The authors rated the evidence as very low quality but said clinicians should be aware of the possible interaction. For other blood thinners, they found no evidence either way, which is not the same as proof of safety.

Medicines to Mention

Bring up every type below that applies to you. This is not a complete list, and it is not a reason to stop any medicine on your own.

Why Your Full List Matters

People often forget things they don't think of as medicine. Vitamins, herbal teas, sleep gummies, allergy pills and a CBD product from a gas station can all count. The FDA says any use of CBD products should be discussed with a health care provider.

The easiest way to get it right is to bring the bottles, or take clear photos of each label. Your list should include:

• Prescriptions, with the dose and time of day you take them.
• Over-the-counter medicines, including ones you take only as needed.
• Vitamins, herbs and other supplements.
• Any CBD or cannabis products you already use, and how you use them.
• How much alcohol you usually drink.

Be honest about cannabis you already use. This is a medical visit, not a test of character, and the clinician can only weigh risks she knows about. If you start cannabis later, tell your pharmacist and your other prescribers too.

Questions to Ask

Write these down and bring them to your evaluation:

• Could cannabis change how any of my current medicines work?
• Which of my medicines add to drowsiness, and how should I plan around that?
• Do I need blood tests, such as INR or liver tests, if I start?
• Should I tell my other prescribers or my pharmacist, and what should I say?
• Would a product with CBD, THC or both fit better with my other medicines?
• Which side effects mean I should stop and call someone?
• Is any amount of alcohol safe while I use cannabis?

Dr. Charlotte Ewals reviews your medicines at every evaluation. She decides whether certification is medically appropriate, and a long medication list does not rule you out. It simply shapes the conversation and the plan.

Next Steps

See what to gather in what to bring to your evaluation, read about starting low and going slow, or learn the difference between CBD and THC. When you are ready, visit our medical cannabis evaluations page or book a visit.