druginteractionsWarfarin is a leading anticoagulant in the management of atrial fibrillation (AF) and deep vein thrombosis (DVT). Multiple drug interactions influence the safety of routine warfarin use and while extensive literature exists regarding the effect on warfarin control and bleeding incidence with many medicines, there is little evidence on the influence of complementary medicines. This study addressed whether the influence of fish and krill oil supplementation had a deleterious impact on warfarin control and bleeding incidence in AF and DVT patients.1

Warfarin works by inhibiting the activation of vitamin K-dependent coagulation Factors V, VII and X in the extrinsic and common pathways of the coagulation cascade. Fish oil works primarily by inhibiting platelet aggregation, stabilizing atherosclerotic plaque, and reducing fibrinogen level, but there is some evidence that it also reduces Factors V and VII in both men and women and Factor X in women. The widespread use of fish oil in the general population for putative benefits in cardiovascular disease as well as other believed benefits (skin, eyes, hair, etc.) has led many patients to take fish oil supplementation as part of their daily health maintenance regimen. Often times, fish oil is taken without consultation with a pharmacist or physician by patients since they can be purchased as an over the counter (OTC) supplemental medication. Hence, it is not uncommon to have patients with AF or DVT take OTC fish oil supplements with a prescribed warfarin regimen. This purpose of this study was to understand whether there was an enhanced or dangerous risk to the patient who concurrently ingested fish oil supplements with their warfarin regimen.

The authors utilized a retrospective analysis methodology to explore this question. This retrospective analysis was undertaken utilizing patient information from a large private pathology clinic. AF and DVT patients receiving long-term warfarin therapy (>30 days) at the clinic and taking fish and krill oil supplements were eligible for study inclusion. Of the 2081 patients assessed, a total of 573 warfarin users met the inclusion criteria with 145 patients in the fish and krill oil group (supplement group) and 428 patients in the control group. Overall, it was found that fish and krill oils did not significantly alter warfarin time in therapeutic range (TTR) or bleeding incidence, even when compared by gender. The authors concluded that omega-3 supplementation with fish and krill oil products does not significantly affect long-term warfarin control and bleeding and thromboembolic events when consumed concurrently in patients managed at an anticoagulation clinic1.

It must be remembered that this very recent study surveyed a very small cohort of patients and lacks the statistical and scientific rigor of an a-priori clinical trial. However the findings of these authors do add to the scientific collection of data that addresses this controversial subject where different findings have been reported on regarding whether or not fish oil supplementation does indeed affect prothrombin times (INR) in patents with AF and DVT.

Readers of this blog are encouraged to read the references listed in the links/reference section found below. Additionally, healthcare practitioners and other interested parties should review data available in the published scientific literature and public domain to understand the complete picture and controversy surrounding this topic. Lastly, before adding any prescription medication, OTC drug or supplement to a daily regimen containing warfarin the patient should always consult first with a pharmacist, physician or other knowledgeable and trained healthcare professional.


  1. Pryce R, et al Nutrients. 2016 Sep 20;8(9). pii: E578
  2. http://afibbers.org/resources/fishoils.pdf