Use of herbal medicines by patients receiving warfarin

Background: Patients receiving warfarin therapy are discouraged from taking herbal medicines. Whether patients adhere to this advice and, if they do not, the types of products they use, are not known. Objective: The objective of this observational study was to estimate the magnitude of use of herbal medicines among Chinese patients attending the Warfarin Clinic of the Prince of Wales Hospital in Hong Kong. Methods: A medical officer interviewed all patients who attended the Warfarin Clinic during May 2001. Patients were asked about the use of herbal medicines in the preceding week. Demographic data, indication and duration of warfarin therapy, and International Normalised Ratio (INR) value at the time of the visit were also noted. Results: Of 107 patients interviewed, 28 (26%) claimed to have taken herbal medicines during the week prior to the clinic visit. The users of herbal medicines had lower INR values than non-users (mean INR value 2.41 +/- 0.65 vs 2.75 +/- 0.65, p = 0.019), possibly because of a lower warfarin dosage (mean dosage 2.93 mg/day +/- 1.23 vs 3.34 mg/day +/- 1.45; p = 0.185) and because a smaller proportion of such patients had heart valve replacement (21% vs 39%, p = 0.141). 'Herbal soup' (soup made at home from vegetables, meat and certain herbs for consumption with the main meals) and 'cool tea' (herbal decoction for the treatment of 'endogenous heat') were the most popular and were taken by 12 (11%) and 11 (10%) patients, respectively. Four patients took proprietary medicines each containing between one and three different herbs that could potentially enhance or antagonise the effects of warfarin. None of the patients in this study showed any evidence of thromboembolism or bleeding on the day of clinic visit. Conclusion: Among Chinese patients treated with warfarin at a Hong Kong clinic, the use of herbal medicines was relatively common. Healthcare professionals play an important role in educating the patients and updating the list of herbal medicines that should be avoided by patients taking warfarin.