Fish Oil as a Blood Thinner: Risks, Interactions, and What You Need to Know
When you take fish oil, a common omega-3 supplement derived from fatty fish like salmon and mackerel. Also known as omega-3 fatty acids, it’s often used for heart health—but it can also act like a mild blood thinner. That’s not just a side effect. It’s a real pharmacological action. If you’re already on warfarin, aspirin, clopidogrel, or any DOAC like apixaban or rivaroxaban, adding fish oil might push your blood too far in the thinning direction. This isn’t theoretical. Emergency rooms see cases every year where people ended up with uncontrolled bleeding after combining fish oil with their blood thinner, often because they thought supplements were "safe."
The anticoagulants, medications designed to prevent dangerous clots in people with atrial fibrillation, deep vein thrombosis, or after heart valve surgery, work by slowing down your body’s clotting process. Fish oil doesn’t work the same way—it reduces platelet stickiness and may slightly lengthen bleeding time. Together, they don’t just add up; they multiply risk. A 2020 study in the Journal of Clinical Lipidology found that people taking over 3 grams of fish oil daily had a 20% higher chance of bleeding complications when also on warfarin. And it’s not just prescription drugs. Even daily aspirin for heart protection can become risky when paired with high-dose fish oil. If you’re scheduled for surgery, your doctor will likely tell you to stop fish oil a week ahead. Why? Because unlike warfarin, there’s no easy test to measure how much fish oil is thinning your blood. You’re flying blind.
And it’s not just about surgery. Think about everyday risks: a fall, a cut that won’t stop bleeding, even a nosebleed that lasts longer than usual. These aren’t just inconveniences—they can be signs your blood is too thin. People over 65, those with liver disease, or anyone on multiple medications are especially vulnerable. You might not realize your fish oil is the hidden factor. That’s why it’s critical to tell every doctor and pharmacist you’re taking it—even if you think it’s "just a supplement." The same goes for other supplements like Ginkgo Biloba, an herb known to increase bleeding risk when combined with anticoagulants. They’re not harmless. They’re part of your medication profile.
So what should you do? If you’re on a blood thinner and taking fish oil, don’t quit cold turkey. Talk to your doctor. They can check your INR or assess your bleeding risk. Maybe you need to lower the dose. Maybe you need to switch to a different omega-3 source. Or maybe you don’t need it at all. The goal isn’t to scare you off fish oil—it’s to make sure you’re not accidentally putting yourself at risk. Below, you’ll find real cases and expert advice on how fish oil interacts with other drugs, what doses matter, and how to stay safe without giving up on heart health.
Fish Oil and Aspirin Together: Do They Increase Bleeding Risk?
Fish oil and aspirin both affect blood clotting, but together they don't significantly increase bleeding risk at standard doses. Large studies show safety for most people, though high doses or surgery require caution.
- December 8 2025
- Tony Newman
- 13 Comments