Fish Oil Pills Aren’t Doing What You Think They’re Doing

OTC options are unhelpful at best, while some prescriptions can raise your arrhythmia risk
Person holding a handful of fish oil capsules after pouring them from a pill bottle.

As a superstar of the supplement aisle, fish oil is said to have all sorts of benefits for your heart health. But does it really live up to the hype?

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It turns out that at best, fish oil pills aren’t likely to do much good for your health — and at worst, they can actually increase your risk for stroke.

Preventive cardiologist Luke Laffin, MD, separates fact from fiction when it comes to fish oil supplements.

What does fish oil do?

Proponents claim that fish oil can lower your risk of heart disease by decreasing blood pressure and cholesterol. That’s because fish oil supplements are a pill form of omega-3 fatty acids, which have been studied for decades and have proven benefits for heart health.

Omega-3 fatty acids are essential nutrients found in fish like herring, wild salmon, bluefin tuna and mackerel. Your body can’t make them on its own, which is why fish that are high in omega-3 fatty acids are such an important part of a healthy diet.

“Populations that eat a lot of fish that contain omega-3 fatty acids have a lower instance of heart disease,” Dr. Laffin notes. Consuming 1 to grams of omega-3s per day can:

Over-the-counter (OTC) fish oil supplements contain a low dose (about 1 gram) of two different omega-3 fatty acids: docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Prescription fish oil pills contain about 4 grams of either a DHA/EPA combo or pure EPA.

Do fish oil supplements work?

When it comes to OTC fish oil supplements, there’s just one caveat: There’s no real proof that they do much of anything.

“We know that people who consume high levels of omega-3 fatty acids by eating fish have a lower risk of cardiovascular events,” Dr. Laffin says, “but that hasn’t been borne out in studies about over-the-counter doses of fish oil.”

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The existing data just isn’t very convincing, he states.

“There have been very large studies done by very reputable organizations, and they just didn’t show any difference in cardiovascular risk reduction or other health benefits.”

Prescription fish oil comes with extra concerns

When it comes to prescription fish oil, there’s some conflicting and controversial information to sort through.

“This is an area of controversy,” Dr. Laffin says. “Many cardiologists have taken the position that the evidence is not very good for the benefits of prescription fish oils. We need more studies in order to be able to give a strong recommendation to take these products.”

A large study showed that people who took a pure-EPA fish oil pill reduced their risk of cardiovascular disease by 25%, compared to people who took a placebo.

That seems like good news. But the placebo was actually not a placebo at all; it was mineral oil, which has since been shown to have some negative cardiovascular effects, like increasing inflammation.

“If the placebo is doing bad things, it may make the drug look good,” Dr. Laffin explains.

A 2021 study found that high doses of fish oil have no effect on reducing major cardiac events in people who are at high risk for them. That study looked at more than 13,000 patients who were already taking statins to lower their cholesterol. The placebo was corn oil, which is thought to be more neutral than mineral oil. That study found no significant reduction in:

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  • Heart attack.
  • Stroke.
  • Death.

The study ended early when researchers found that fish oil wasn’t showing any benefits and was shown to increase chances of atrial fibrillation, a form of arrhythmia (irregular heartbeat) that can lead to a stroke.

“People who are at a high risk for heart disease don’t have a whole lot of great treatment options aside from statins, so in some cases, the benefits of pure EPA fish oil may outweigh potential risks,” Dr. Laffin says, “but I prescribe it very sparingly.”

Fish oil side effects

Taking OTC supplements is always risky, as they’re not regulated by the U.S. Food and Drug Administration (FDA).

“You want to take medications that have proven benefits,” Dr. Laffin advises. “When it comes to fish oil, at best you’re just losing money on supplements that don’t do anything. At worst, they can have negative impacts.”

Some fish oil supplements have been tested by consumer organizations and found to be contaminated with mercury. And even safe, low-dose fish oil supplements (though again, there’s no way to tell!) can have unpleasant side effects, including:

  • A fishy aftertaste, including “fish burps.”
  • Bad breath.
  • Nausea.
  • Upset stomach.

Higher-dose prescription fish oil comes with additional risks:

  • Atrial fibrillation: Prescription fish oil comes with an increased risk of atrial fibrillation, an irregular heart rhythm that can lead to a stroke.
  • Bleeding: Fish oil can also increase your risk of bleeding.

If you’re at high risk for heart disease, talk to your doctor about the best options for lowering your risk. And if you just want to be sure you’re getting all the benefits of omega-3 fatty acids, it’s best to skip the fish oil supplements and just make salmon for dinner instead.

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