Does CBD interact with warfarin (blood thinners)?

Yes — CBD has a clinically significant interaction with warfarin. CBD inhibits CYP2C9, the primary enzyme responsible for warfarin metabolism. This inhibition increases warfarin blood levels, potentially raising INR (international normalized ratio) and bleeding risk. Multiple case reports document INR elevation in patients who added CBD to stable warfarin regimens. In one case series, INR increased from therapeutic range (2–3) to supratherapeutic levels (>4) within weeks of starting CBD. The interaction is dose-dependent and more pronounced at higher CBD doses. Patients on warfarin who use CBD require more frequent INR monitoring and likely warfarin dose reduction. This interaction extends to other CYP2C9 substrates including phenytoin, losartan, and some NSAIDs.