Omega-3 Safety: Medicines, Atrial Fibrillation, Allergies, High Doses and Product Quality

Overview

For most people, omega-3 supplements cause only mild side effects, but concentrated oils are not risk-free. NCCIH lists unpleasant taste, bad breath, bad-smelling sweat, headache, heartburn, nausea and diarrhea as the usual effects. [1] The sections below cover what is more serious. This page gives general information; it does not tell you to stop or change any medicine. Talk to your prescriber or pharmacist first: Talking with a health professional.

Medicines and bleeding

• The Lovaza prescription label says omega-3 acids may prolong bleeding time and that people taking an anticoagulant or another drug affecting clotting (for example antiplatelet agents) should be monitored periodically. It adds that bleeding-time changes in trials did not exceed normal limits or cause clinically significant bleeding. [2]
• The Vascepa label (4 g a day of purified EPA) reports bleeding events in 12% of treated patients versus 10% on placebo, serious bleeding in 3% versus 2%, and more bleeding in people also taking aspirin, clopidogrel or warfarin. [3]
• In the VITAL trial, 1 g a day of marine omega-3 produced no excess risk of bleeding or other serious adverse events. [4]
• Evidence label: mixed, and dose-dependent. Over-the-counter products are not the same as these medicines, but the labels show why clinicians ask about fish oil. See how interactions work and interactions by drug class.
• Before surgery: NCCIH says certain supplements may increase bleeding risk and you should tell your providers as early as possible. [5] See Supplements before surgery.
• Flaxseed oil: NCCIH says there are theoretical reasons it might interact with anticoagulant or antiplatelet drugs. [6]

Atrial fibrillation (irregular heartbeat)

A 2021 meta-analysis of 7 trials (81,210 adults, average age 65) found marine omega-3 supplements associated with more atrial fibrillation (hazard ratio 1.25, 95% CI 1.07 to 1.46). The ratio was 1.49 in trials of more than 1 g a day and 1.12 at 1 g or less. [7] In REDUCE-IT, hospitalization for atrial fibrillation or flutter was 3.1% with icosapent ethyl versus 2.1% with placebo. [8] The Lovaza label notes a possible link with recurrences of symptomatic AF in people who already have it. [2] If you have a heart rhythm condition, ask your cardiology team before using any omega-3 product.

High doses

EFSA (EU) did not set an upper intake level because data were insufficient, but concluded supplemental EPA plus DHA up to 5 g a day do not raise safety concerns for adults, including for bleeding, blood sugar control or immune function. [9] That conclusion is about adults, in a different regulatory system from the US. Higher is not better: the atrial fibrillation risk rose with dose. [7]

Fish and shellfish allergy

Both prescription labels say it is not known whether people with fish or shellfish allergy are at higher risk of reaction, and advise caution; Vascepa's label says to stop it and seek medical attention if a reaction occurs. [3][2] Algal oil comes from algae and not from fish. [1] For krill products we did not find a source specific to shellfish allergy: Proper evidence not found, so ask your allergist.

Cod liver oil and added vitamins

NCCIH says fish liver oil supplements contain vitamins A and D in amounts that vary and that both can be harmful in excessive amounts. [1] The NHS (UK) says an average of 1.5 mg (1,500 micrograms) of vitamin A a day or less from food and supplements combined is unlikely to cause harm, lists fish liver oil among high-vitamin-A supplements, and advises avoiding fish liver oil supplements in pregnancy or when trying for a baby unless a GP advises otherwise. [10][11] See cod liver oil and vitamin A.

Pregnancy and children

Discuss any omega-3 product with your maternity provider. The NHS advises no more than two portions of oily fish a week in pregnancy because of pollutants. [11] See Pregnancy and breastfeeding.

Product quality

A market study of fish oil capsules found variation in oxidation, odor and whether EPA and DHA matched the label. [12] See how to read a fish oil label and Product quality and contamination.

Report problems

See Side effects, allergic reactions and reporting.