Unveiling the impact of water-boiled cannabis on warfarin: A case report of atrial fibrillation patients after cannabis legalization in Thailand

Warfarin, a commonly prescribed anticoagulant, is utilized to prevent thrombotic issues and requires careful dose adjustment due to its narrow therapeutic range. As warfarin is metabolized by essential drug-metabolizing enzymes (DMEs), it is prone to interactions with a wide range of therapeutic agents, including herbal medicines. In June 2022, Thailand became the first country in Asia to remove cannabis plants from its narcotics control list, allowing individuals to cultivate them for personal use. Consequently, this report aimed to examine the interaction between cannabis and warfarin in Thai patients following the legalization of cannabis from 2021 to 2023. These three case reports elucidated the potential for drug interactions arising from the concurrent use of warfarin and water-boiled cannabis. This process involved placing cannabis flowers into a boiling kettle and subsequently consuming the resulting cannabis-infused water instead of regular drinking water. Our findings revealed that each atrial fibrillation patient had supratherapeutic international normalized ratio (INR) levels ranging from 3.49 to 4.92, with no bleeding complications. Following the cessation of cannabis use, the INR levels decreased and returned to the therapeutic range for warfarin therapy. In summary, the current report indicates that water-boiled cannabis may influence the outcomes of warfarin therapy, as evidenced by the changes in INR levels.