Possible Interaction Between Hibiscus and Warfarin Resulting in Severe International Normalized Ratio Elevation: A Case Report.

Warfarin has a narrow therapeutic window and is susceptible to interactions with medications, foods, and herbal products. We describe the case of a 59-year-old woman with a mechanical mitral valve receiving chronic warfarin therapy who developed a markedly elevated international normalized ratio (INR) after recently consuming hibiscus tea. No other clear precipitating factor for the supratherapeutic INR was identified. Warfarin was temporarily withheld, hibiscus intake was discontinued, and oral vitamin K was administered with subsequent normalization of the INR. This case highlights the importance of obtaining a thorough dietary and herbal history in patients receiving warfarin therapy and raises awareness of a possible interaction between warfarin and hibiscus products.