Warfarin and Chinese Herbs: Concern or Knee-jerk Conservatism?

Warafrin is commonly thought to be contraindicated for use with concurrent Chinese herbal therapy. Is this view is substantiated or is it part of a trend to create problems that don’t exist with false contraindications? Let’s look at a few studies.

Observational Cohort Research: “Use of herbal medicines by patients receiving warfarin.” http://www.ncbi.nlm.nih.gov/pubmed/12825970

The goal of this study was to observe how common it is for patients to take herbs while taking warfarin and what kinds of problems occurred as a result, if any. Of the 107 patients interviewed, approximately 25% used herbs while taking warfarin, mostly in the form of food based delivery. At least three patients took herbs that are considered to be potentially antagonistic or enhancive to the effects of warfarin. In all cases they observed “no evidence of thromboembolism or bleeding on the day of clinic visit.”This study correlates to others that have investigated potential herb-warfarin interactions.

There is a prevailing trend to over focus on in vitro studies and theoretical concerns about drug-herb interactions that do not account for the complex interactions found in Chinese herbal formulations. The evidence thus far is mostly limited to clinical observation, and if it herb-warfarin interactions do occur they are relatively rare.i,ii

Observational studies such as these raise questions about the occurrence and relevance of these interactions in context of actual TCM treatment. Herbs such as sheng jiang and dang gui, for example, may not pose a threat when used at recommended dosages.iii It is prudent to be cautious and informed as a clinician when dealing with such medications; however, the proposed risk assessment is yet highly subjective and must be further investigated with larger population samples in order to be brought more in line with actual clinical outcomes.iv

[i] http://www.ncbi.nlm.nih.gov/pubmed/15801937

[ii] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3976951/

[iii] http://www.ncbi.nlm.nih.gov/pubmed/18374198

[iv] http://www.ncbi.nlm.nih.gov/pubmed/23671711

[v] http://www.ncbi.nlm.nih.gov/pubmed/22292789

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