Fish Oil Side Effects
Fish Oil Side Effects
Fish oil supplements are generally well tolerated when used in ordinary amounts, but they can cause side effects in some people. The most common problems are mild and related to the digestive system.
Common Side Effects
Possible side effects of fish oil and other omega-3 supplements include a fishy aftertaste, bad breath, heartburn, nausea, stomach discomfort and diarrhea. Some people also experience fishy-tasting burps after taking capsules.
These effects may depend on the product, dose and individual tolerance. Taking a supplement with food or dividing the daily amount into smaller servings may make it easier to tolerate.
Fish Oil and Bleeding
EPA and DHA can influence platelet activity, which is why fish oil is often described as having a “blood-thinning” effect. However, normal supplemental amounts have not been shown to cause clinically significant bleeding in most people.
People taking anticoagulant or antiplatelet medications should nevertheless discuss high-dose omega-3 supplementation with a healthcare professional, particularly when using therapeutic amounts rather than ordinary dietary supplements.
High-Dose Omega-3 Supplements
More fish oil is not necessarily better. High doses are sometimes used medically to lower triglycerides, but therapeutic omega-3 treatment should be distinguished from ordinary over-the-counter supplements.
Several large clinical trials using approximately 4 grams per day of omega-3 fatty acids found a small increase in atrial fibrillation among people with cardiovascular disease or a high cardiovascular risk. This does not mean that ordinary amounts of fish oil cause atrial fibrillation, but it is another reason not to treat high-dose supplementation as routine self-care.
For more information about amounts of EPA and DHA, see Dosage of Fish Oil.
Cod Liver Oil Is Different
Cod liver oil provides EPA and DHA but also naturally contains vitamins A and D. Excessive intake of cod liver oil can therefore create risks that do not apply in the same way to ordinary fish oil, particularly excessive intake of preformed vitamin A.
If several supplements are being used at the same time, it is worth checking their labels so that vitamin A and vitamin D are not unintentionally duplicated.
Fish Allergy and Product Ingredients
People with an allergy to fish or shellfish should check with a healthcare professional before using marine omega-3 products. Supplement capsules may also contain gelatin, flavorings, antioxidants or other ingredients unrelated to the fish oil itself.
When Medications Are Involved
Fish oil supplements can interact with some medications. This is particularly relevant with anticoagulants and other drugs affecting blood clotting, as well as when large omega-3 doses are being considered for a medical condition.
The NIH Office of Dietary Supplements provides detailed information about omega-3 supplement safety, doses and medication interactions.
This page provides general information about fish oil supplements and is not a substitute for individualized medical advice.