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In Reply Dr Harris, who owns a company that produces an assay to assess ω-3 levels, asserts that the potential increased bleeding risk associated with the concurrent use of ω-3 fish oils and warfarin is a legend that is not evidence based. The evidence he provides to support this assertion is derived from studies that took place among postsurgical patients that are underpowered to detect such an association.
In contrast to these studies, several case reports demonstrate extremely elevated international normalized ratios and increased bleeding risk associated with the use of ω-3 fish oils with warfarin.1,2 These findings are consistent with both in vitro and in vivo animal and human studies suggesting the anticoagulant effects of these drugs.1,2 Micromedex, the drug compendium and the source for our data on potential drug-drug interactions, acknowledges the lack of well-controlled clinical trials and lists the use of ω-3 fish oils in combination with warfarin as a potentially major, or life-threatening, drug interaction due to increased bleeding risk.3
Qato DM, Alexander GC. Fish Oils and Bleeding—Where Is the Evidence?—Reply. JAMA Intern Med. 2016;176(9):1406-1407. doi:10.1001/jamainternmed.2016.3971