Healthy fats are essential—but doctors flag potential side effects to keep in mind if you're taking them in supplement form.
Omega-3 fatty acids aren’t just a “nice-to-have” in your diet. These healthy fats are important players in everything from heart and brain function to joint and eye health. There are some nutrients, like vitamin D, that a healthy body is able to synthesize on its own, but omega-3 is something we need to get through our diets. Omega-3 foods include fish like salmon, mackerel, and sardines, as well as in plant-based sources such as flax seeds, walnuts, and chia seeds.
With the cultural awareness that omega-3 fats are important to our health, many Americans have turned to nutrition supplements in capsule or other form to increase their omega-3 intake. Research suggests that omega-3 supplements alone do not reduce heart disease risk. Instead, studies show that consuming seafood one to four times per week may reduce the risk of death from heart-related conditions.
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According to the Cleveland Clinic, it’s generally preferable to get omega-3s from whole food sources rather than supplements. For individuals with high triglycerides or those diagnosed with rheumatoid arthritis, omega-3 supplements like fish oil pills may offer certain benefits.
As with any supplement, it’s best to consult a healthcare provider before you start on omega-3. Although side effects are typically mild and rare, higher doses may come with more serious risks.
Below, we review potential omega-3 side effects.
What are the major side effects of omega-3?
1. Bleeding risk
Omega-3 fatty acids are generally safe, but they can have side effects when consumed in high doses. One potential risk, as noted by the Cleveland Clinic, is an increased chance of bleeding, particularly with higher-dose prescription fish oil. This is because omega-3s act as natural anticoagulants, which means they can slightly reduce blood clotting by affecting platelet function.
A recent review published in May 2024 in the peer-reviewed Journal of the American Heart Association examined whether omega-3 supplements increase bleeding risk, specifically in relation to dosage and concurrent use of blood-thinning medications. Researchers analyzed data from 11 randomized clinical trials with 120,643 participants up to May 2023.
The study found that omega-3 polyunsaturated fatty acids (PUFAs) generally do not increase bleeding risk. However, those taking high doses of purified eicosapentaenoic acid (EPA), a specific type of omega-3, may face a slight increase in bleeding risk—though this effect is minor and likely not clinically significant.
Before starting an omega-3 supplement, it’s important to consult your healthcare provider, especially if you have a history of bleeding disorders, are taking blood-thinning medications, or have an upcoming medical procedure. Your doctor can advise on the safest dosage or suggest alternatives to help minimize any potential risks.
2. Atrial fibrillation
Atrial fibrillation (AFib) is another potentially serious side effect linked to prescription fish oil-based omega-3 supplements. AFib is a type of irregular heartbeat that raises the risk of blood clots, stroke, and heart failure. A recent study published in May 2024 in the peer-reviewed British Medical Journal examined whether regular fish oil supplementation influences the risk and progression of cardiovascular disease. This study tracked over 415,000 participants across different stages of heart health.
For generally healthy individuals, the findings suggested that regular fish oil supplementation might slightly increase the risk of developing AFib or having a stroke. However, in participants with existing heart conditions, fish oil appeared to offer protective benefits, potentially slowing the progression from AFib to more severe complications and lowering the risk of heart failure-related death. These results imply that fish oil’s effects on heart health may vary depending on a person’s cardiovascular status, highlighting the need for further research.
3. Gastrointestinal issues
Omega-3 supplements can sometimes cause digestive discomfort, including symptoms like heartburn, nausea, and diarrhea, according to the National Institutes of Health. This is partly because omega-3 fatty acids can have a mild laxative effect and are high in fat, which some people may find harder to digest.
To help ease these symptoms, consider starting with a lower dose and gradually increasing it over time. Taking your omega-3 supplements with meals can also improve digestion and reduce the chance of discomfort.
4. Fishy aftertaste
A fishy aftertaste—and sometimes even “fish burps”—can be an unwelcome side effect of fish oil-based omega-3 supplements, according to the Mayo Clinic. To minimize these effects, opt for high-quality, purified supplements, ideally with an enteric coating, which helps them bypass the stomach and dissolve in the intestines instead. Taking omega-3 supplements with meals can also reduce the aftertaste.
If you notice a strong, unpleasant odor from your supplement, it may be a sign the oil has gone rancid. Rancid fish oil not only tastes unpleasant but also loses potency and can produce harmful compounds. In this case, it’s best to discard the supplement and replace it with a fresh, high-quality product. For optimal freshness, always store omega-3 supplements in a cool, dark place.
5. Immune system effects
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Omega-3 fatty acids are known to support immune health by reducing inflammation, strengthening cell membranes, and encouraging healthy immune cell activity. However, research suggests that consuming very high doses of omega-3s could actually dampen certain immune responses. This effect is dose-dependent, meaning it’s more likely to occur when omega-3 intake exceeds the recommended daily amount.
The National Institutes of Health recommends a daily intake of 1.1 to 1.6 grams of omega-3s, while the American Heart Association advises including two servings of fish (about three to four ounces each) per week as part of a heart-healthy diet. The US Food and Drug Administration recommends keeping omega-3 intake from supplements (combined EPA and DHA) to no more than five grams per day.
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