My cardiologist has me on warfarin (Coumadin) for atrial fibrillation. I've been reading about CBD for anxiety and sleep, but I'm worried about interactions. My doctor isn't very familiar with cannabis. Is it safe to take CBD while on warfarin? What does the research say?
Medical Disclaimer: Answers in this forum are for educational purposes only and do not constitute medical advice. Always consult your healthcare provider before making changes to your treatment.
Medical Science Editor, PharmD
This is one of the most important drug interaction questions in cannabis medicine, and you are right to be cautious.
CBD is metabolized by the cytochrome P450 enzyme system — specifically CYP2C9, which is the same enzyme that metabolizes warfarin. When CBD inhibits CYP2C9, it slows warfarin metabolism, causing warfarin blood levels to rise. This increases your INR (International Normalized Ratio) and your bleeding risk.
Multiple case reports have documented this interaction. A 2019 case report in Epilepsy & Behavior described a patient on warfarin whose INR nearly doubled after starting CBD oil. A 2020 review in Cannabis and Cannabinoid Research identified warfarin as one of the highest-priority drug interactions for CBD.
The interaction is dose-dependent. Low-dose CBD (under 25mg/day) may have minimal effect on INR in some patients, but there is significant individual variability. High-dose CBD (150mg+, as used for epilepsy) reliably increases INR.
1. Do not start CBD without telling your cardiologist — even if they are not familiar with cannabis
2. If your cardiologist approves a trial, start with the lowest possible dose (5–10mg CBD)
3. Check your INR more frequently when starting, stopping, or changing CBD dose
4. Use a reputable CBD product with a Certificate of Analysis — contaminated products can have unpredictable effects
5. Consider CBD-free alternatives for anxiety/sleep that do not interact with warfarin
Bottom Line: The interaction is real and clinically significant. This does not mean you can never use CBD, but it requires careful medical supervision and INR monitoring. Please use our Drug Interaction Checker and bring the results to your cardiologist.
Verified Pharmacist
Dr. Rodriguez's answer is excellent. I want to add a practical pharmacist perspective.
The warfarin-CBD interaction is well-documented enough that I flag it for every patient who asks. The mechanism (CYP2C9 inhibition) is the same reason grapefruit interacts with warfarin — CBD is actually a stronger inhibitor than grapefruit juice for this enzyme.
If your cardiologist is open to a trial, ask about starting with topical CBD first — it has very low systemic absorption and is unlikely to affect INR. This can help you assess whether CBD helps your symptoms before taking on the interaction risk of oral CBD.
Also worth noting: THC has a different metabolic pathway (primarily CYP3A4) and a less well-characterized interaction with warfarin, but there are case reports of INR changes with THC as well. The safest approach is to avoid all cannabinoids until you have a clear plan with your cardiologist.
Community Member
I'm in a similar situation — AFib on warfarin. My cardiologist was initially dismissive but I brought printed research and she agreed to monitor my INR closely if I tried CBD. I started at 10mg/day and my INR went from 2.4 to 3.1 within 3 weeks. We reduced my warfarin dose slightly and my INR stabilized. I've been on CBD for 8 months now with stable INR and it has genuinely helped my anxiety.
The key was having a cardiologist willing to monitor. Don't try this without medical supervision — the interaction is real.