Fish Oil, Blood Thinners and Bleeding Risk: Warfarin, Aspirin, Anticoagulants and Surgery
What drug labels, trials and case reports say about fish oil with warfarin, aspirin and other blood thinners, and what to tell your surgical team, without any advice to stop a medicine.
Content last updated . This page has not been medically reviewed.
How the sources define the question
The labels name two groups of "blood thinners": anticoagulants such as warfarin, and antiplatelet medicines such as aspirin and clopidogrel. [1] Prescription omega-3 labels say omega-3 acids may prolong bleeding time and advise periodic monitoring of people also taking an anticoagulant or antiplatelet drug. They add that the longer bleeding time seen in trials did not exceed normal limits or cause clinically significant bleeding. [2] Prescription EPA, mixed EPA and DHA products, over-the-counter fish oil, krill oil and algal oil are different products, so we label each finding with what was tested.What studies found
Evidence labels: mixed (studies disagree), insufficient (too little good research), case report (one patient, cannot show cause).| Question | What the source found | Strength |
|---|---|---|
| Prescription EPA with antithrombotic drugs | In an 8,179-patient trial of icosapent ethyl, 12% had a bleeding event versus 10% on placebo; serious bleeding 3% versus 2%; bleeding was greater in people also taking aspirin, clopidogrel or warfarin. [1] | Trial data in a high-risk group on a prescription product |
| Pooled bleeding risk across trials | 11 trials, 120,643 patients: no difference in overall bleeding (rate ratio 1.09, 95% CI 0.91 to 1.31). High-dose purified EPA showed a 50% relative and 0.6% absolute increase. Bleeding risk tracked EPA dose, not background antiplatelet use. [3] | Meta-analysis; mixed by product |
| Fish oil with chronic warfarin | 16 patients on stable warfarin got placebo, 3 g or 6 g of fish oil daily for 4 weeks; no statistically significant INR change, one bruising episode, no major bleeding. [4] | Small randomized trial; insufficient |
| Fish and krill oil users on long-term warfarin | In a retrospective review of 573 warfarin users at one clinic (145 taking fish or krill oil, 428 not), the authors concluded the oils did not significantly affect warfarin control, bleeding or clotting events. [5] | Observational; amounts not controlled |
| Warfarin and fish oil, one patient | A 67-year-old woman's INR rose from 2.8 to 4.3 after she doubled her fish oil from 1,000 to 2,000 mg a day; it fell after she cut back. [6] | Case report |
| High-dose omega-3 with warfarin and aspirin | A case report describes a bleed inside the head after a minor fall in an older patient taking 6 g a day with both drugs; the authors said the combination likely contributed. [7] | Case report |
| Single warfarin dose with prescription EPA | In 25 healthy adults, 4 g a day of icosapent ethyl did not significantly change warfarin levels or INR effects. [8] | Phase 1 study in healthy people |
Biomarker change (INR, the clotting blood test used with warfarin, or bleeding time) is not the same as a bleeding event, and healthy volunteers do not tell us what happens in older patients on several medicines.
Surgery and procedures
NCCIH says certain dietary supplements may increase the risk of bleeding or affect your response to anesthesia, and advises telling your providers about all supplements as early as possible. [9] Studies:- In a trial of 1,516 patients having heart surgery, fish oil (8 to 10 g a day for 2 to 5 days before surgery, then 2 g a day after) did not increase major bleeding compared with placebo (odds ratio 0.81, 95% CI 0.53 to 1.24). [10] These are study amounts in a monitored hospital setting, not advice.
- In a small review of 28 spinal fusion patients, those who had taken omega-3 and stopped it on average 5.2 days before surgery had blood loss similar to controls. [11]
These studies do not replace your surgeon's instructions, which can differ by procedure and medicines. Whether to stop a supplement before surgery is for the surgical and anesthesia team to decide. See Supplements before surgery.
Limits and uncertainty
Most bleeding data come from prescription products at 4 g a day or from trials not designed to test interactions. Proper evidence not found: our PubMed searches for randomized trials of over-the-counter fish oil added to aspirin plus clopidogrel, and for fish oil with newer oral anticoagulants (apixaban, rivaroxaban, dabigatran), returned no usable trial.Safety and who should ask
Ask a pharmacist or prescriber before using fish oil if you take warfarin or another blood thinner, have a bleeding disorder, are older, or have surgery or dental work planned. Also tell them about cod liver oil, krill oil and flaxseed oil. See Medication interactions, the omega-3 interaction table, and the safety overview.Frequently asked questions
Does fish oil interact with warfarin?
Evidence is mixed. One small randomized trial found no significant INR change at 3 to 6 g a day and a retrospective review found no significant effect on warfarin control, while case reports describe a higher INR or bleeding in individual patients. Tell your anticoagulation clinic or pharmacist about any fish oil. [4][5][6][7]
Is it safe to take fish oil with aspirin?
Labels for prescription omega-3 products say bleeding was greater in people also taking aspirin, clopidogrel or warfarin, while a pooled analysis found bleeding tracked EPA dose rather than antiplatelet use. Ask your prescriber. [1][3]
Should I stop fish oil before surgery?
That is for your surgical and anesthesia team to decide. NCCIH says to tell your providers about every supplement early. A trial in heart-surgery patients found no extra major bleeding with fish oil. [9][10]
Does krill oil or algal oil have the same effect?
Krill oil was grouped with fish oil in one retrospective warfarin review, which found no significant effect on warfarin control. Proper evidence not found for algal oil: our PubMed search for algal oil with warfarin or bleeding returned nothing, so ask a pharmacist. [5]
Does omega-3 from food affect bleeding?
Not described in the sources we read for this page: our PubMed search for oily fish diet and warfarin INR returned nothing usable. Ask your clinician or pharmacist.
References
- FDA prescribing information for icosapent ethyl capsules, via openFDA drug label API (label effective 2026-03-23). Read 2026-10-23.
- FDA prescribing information for omega-3-acid ethyl esters capsules, via openFDA drug label API (label effective 2023-10-06). Read 2026-10-23.
- Javaid M et al., Bleeding Risk in Patients Receiving Omega-3 Polyunsaturated Fatty Acids: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. J Am Heart Assoc 2024. Read 2026-10-23.
- Bender NK et al., Effects of Marine Fish Oils on the Anticoagulation Status of Patients Receiving Chronic Warfarin Therapy. J Thromb Thrombolysis 1998. Read 2026-10-23.
- Pryce R et al., The Use of Fish Oil with Warfarin Does Not Significantly Affect either the International Normalised Ratio or Incidence of Adverse Events in Patients with Atrial Fibrillation and Deep Vein Thrombosis: A Retrospective Study. Nutrients 2016. Read 2026-10-23.
- Buckley MS et al., Fish oil interaction with warfarin. Ann Pharmacother 2004 (case report). Read 2026-10-23.
- McClaskey EM, Michalets EL, Subdural hematoma after a fall in an elderly patient taking high-dose omega-3 fatty acids with warfarin and aspirin: case report. Pharmacotherapy 2007. Read 2026-10-23.
- Braeckman RA et al., Phase 1 study of the effect of icosapent ethyl on warfarin pharmacokinetic and anticoagulation parameters. Clin Drug Investig 2014. Read 2026-10-23.
- NCCIH, Using Dietary Supplements Wisely. Read 2026-10-23.
- Akintoye E et al., Fish Oil and Perioperative Bleeding. Circ Cardiovasc Qual Outcomes 2018. Read 2026-10-23.
- Meredith DS et al., The effect of omega-3 fatty-acid supplements on perioperative bleeding following posterior spinal arthrodesis. Eur Spine J 2012. Read 2026-10-23.