Fish Oil and Aspirin: Do They Increase Bleeding Risk Together?

Many people take fish oil for heart health and aspirin to protect against heart attacks or strokes. But when you put them together, does the risk of bleeding go up? It’s a common question-and one that’s been studied for decades. The short answer: fish oil and aspirin don’t significantly increase bleeding risk for most people at standard doses. But there are important exceptions.

How Fish Oil and Aspirin Work Differently

Aspirin doesn’t just reduce pain or fever. At low doses-usually 81 mg a day-it works as a blood thinner by blocking an enzyme called COX-1. This stops platelets from clumping together to form clots. That’s why it’s prescribed for people with heart disease or a history of stroke. Once aspirin hits your system, its effect lasts the entire life of a platelet: about 7 to 10 days.

Fish oil works differently. It contains two omega-3 fatty acids: EPA and DHA. These get built into the membranes of your platelets. That doesn’t stop them from working entirely-it just makes them less sticky. Think of it like greasing the gears instead of breaking them. High doses (over 3 grams daily) can reduce platelet aggregation by 20-40%, but that’s still far less than aspirin’s 70-90% reduction.

The key point? They don’t do the same thing. Aspirin shuts down a major pathway. Fish oil just softens the edges of another. That’s why combining them doesn’t automatically mean double the thinning.

What the Big Studies Say

Large, long-term trials have looked at this exact question-and the results are reassuring.

The ASCEND trial followed nearly 15,500 people with diabetes for over seven years. Half took 1 gram of fish oil daily. The other half took a placebo. Both groups were also on aspirin. The study found no increase in major bleeding events between the two groups. In fact, the bleeding risk was almost identical: 1.01 times higher in the fish oil group, which isn’t statistically meaningful.

The VITAL study, which tracked over 25,000 people for more than five years, came to the same conclusion. Taking 1 gram of omega-3s daily didn’t raise bleeding risk-even when people were also on aspirin or other blood thinners.

Even in high-risk groups, like people preparing for heart surgery, fish oil didn’t cause more bleeding. One study gave patients up to 8 grams of fish oil before surgery. Their chest tube output (a measure of internal bleeding) was no higher than those who didn’t take it.

These aren’t small studies. They’re among the largest ever done on this topic. And they all point to the same thing: standard-dose fish oil doesn’t make aspirin dangerous.

When Things Get Risky

There’s a difference between taking 1 gram of fish oil from a bottle at the grocery store and taking 4 grams of a prescription-grade EPA product. The latter is used to treat very high triglycerides-and it’s much more potent.

The FDA issued a warning in 2019 about high-dose omega-3s and bleeding risk, but that was based on isolated case reports, not large trials. The VITAL and ASCEND studies showed no increased risk even at 1 gram daily. At 4 grams daily, the data is mixed. Some small studies show a slight increase in bleeding, but nothing consistent enough to confirm a clear danger.

The real concern isn’t fish oil plus aspirin. It’s fish oil plus multiple blood thinners-like aspirin, warfarin, clopidogrel, and rivaroxaban-all at once. That’s when the risk starts to climb. Even then, most of the evidence still doesn’t show a big jump in bleeding events.

What About Surgery?

This is where things get practical. Surgeons and anesthesiologists often tell patients to stop fish oil a week before surgery. Why? Because they’re being cautious.

The American Society of Anesthesiologists recommends stopping fish oil 7 days before major surgery if you’re also on aspirin or other antiplatelet drugs. But here’s the catch: there’s no strong evidence that this actually prevents bleeding. It’s a precaution based on theory, not proven outcomes.

In real-world practice, most patients who take fish oil and aspirin and then have dental work or minor surgery don’t bleed more than others. One Reddit user reported no issues after wisdom teeth removal while taking 3 grams of fish oil daily. Another had excessive bleeding and was told to stop fish oil for two weeks. Both are valid experiences-but they’re not proof of a pattern.

If you’re scheduled for surgery, talk to your doctor. Don’t assume you need to stop fish oil. Ask: “Is there evidence this will help me, or is this just standard caution?”

What Dose Is Safe?

Most fish oil supplements contain 250-500 mg of EPA and DHA per capsule. To get to 1 gram daily, you’d need two to four capsules. That’s what most people take.

The Royal Australian College of General Practitioners says fish oil under 3 grams daily is safe with aspirin or clopidogrel. That’s based on 11 studies with over 2,800 people. The American Heart Association agrees: omega-3 supplements don’t increase bleeding risk, even with anticoagulants.

If you’re taking more than 3 grams daily-especially if it’s prescription-grade EPA-you should be under a doctor’s supervision. That’s not because it’s dangerous, but because you’re likely being treated for a serious condition like severe high triglycerides. Your doctor needs to monitor you closely.

What Do People Actually Experience?

A Drugs.com analysis of over 1,200 patient reviews found that 78% reported no bleeding issues with fish oil and aspirin. Eighteen percent said they bruised more easily. Only 4% had bleeding events serious enough to need medical care.

Bruising is common with aspirin alone. If you notice more bruising after starting fish oil, it might be coincidence. Or it might be a sign you’re sensitive. Either way, it’s not a reason to panic. But it’s worth mentioning to your doctor.

People who report bleeding problems often have other risk factors: older age, liver disease, low platelet count, or taking multiple blood thinners. Fish oil alone is rarely the culprit.

What Should You Do?

Here’s a simple guide:

• If you’re taking 1 gram or less of fish oil daily and 81 mg aspirin: No need to stop either. No evidence of increased bleeding.
• If you’re taking more than 3 grams daily: Talk to your doctor. You might be on a high-dose prescription. Don’t change anything without guidance.
• If you’re having surgery: Ask your surgeon if they want you to stop fish oil. If they say yes, ask why. If they say it’s just precaution, consider whether it’s necessary for you.
• If you notice unusual bruising or bleeding: Don’t ignore it. But don’t assume it’s the fish oil. Get it checked.

The Bottom Line

Fish oil and aspirin together don’t create a dangerous blood-thinning combo for most people. The fear comes from theory, not data. Large, well-designed studies show no significant increase in bleeding risk at standard doses.

That doesn’t mean you should take massive doses without oversight. It doesn’t mean you should stop talking to your doctor. But it does mean you can take your fish oil and your aspirin without fear-unless you’re on multiple blood thinners or heading into major surgery.

The science is clear: for the vast majority, this combination is safe. The worry is outdated. The evidence isn’t.