Is There Any Danger When Taking Omega-3? Who Should Ask First

For most adults there is no danger in taking omega-3 at supplement doses: in a five-year trial of 840 mg of EPA and DHA a day, side effects were no different from placebo, and EFSA concluded that supplemental EPA and DHA up to 5 g a day raise no safety concern for adults. The cautions are specific and the table below lists them; the two most asked about are anticoagulants and doses above 1 g a day.^{1, 2, 3, 4, 16}

• Ask first: anticoagulant or antiplatelet medicines; surgery; a heart rhythm problem with doses above 1 g; pregnancy; children's doses
• Atrial fibrillation: about 50% more likely above 1 g a day in trials, about 12% at 1 g or less

Sources checked on 29 October 2026.

Who should not take omega-3?

Almost nobody is ruled out; a few people should ask first.

Algal DHA raised blood DHA as well as cooked salmon did, which makes it the route for a fish allergy or a vegan diet; compare an algal capsule or gummy's label figure with the 250 mg of DHA a day behind the register's brain and vision wording.^{6, 8}

Does omega-3 thin the blood?

Slightly, in the laboratory; not in a way that has shown up as bleeding. EPA and DHA make platelets a little less likely to clump.¹ A systematic review of 52 studies found that fish oil did not increase bleeding or transfusion during or after surgery and saw no need to stop it beforehand.¹

Can too much omega-3 cause bleeding?

At prescription doses, a little. In REDUCE-IT, 4 g of purified EPA a day in 8,179 statin-treated people with high triglycerides produced serious bleeding in 2.7% against 2.1% on placebo, short of statistical significance.⁹ So 4 g belongs with a doctor; if you take an anticoagulant, tell your GP or anticoagulant clinic, keep the daily dose steady, and report unusual bruising or nosebleeds. The NHS tells people on warfarin to let their doctor know about any vitamins or supplements they take.¹⁰

Does fish oil cause atrial fibrillation?

At high doses it can. Across seven cardiovascular trials in 81,210 people, those given omega-3 were about 25% more likely to develop atrial fibrillation than those on placebo, and the effect depended on dose: about 50% higher in trials using more than 1 g of EPA and DHA a day, about 12% higher at 1 g or less.² The VITAL Rhythm trial, 840 mg a day in more than 25,000 adults for five years, found no significant increase.⁴ How much omega 3-6-9 you need a day has the dose marks.

Why is fish oil "no longer recommended"?

The headline comes from a 2024 UK Biobank cohort study in which regular fish oil users had a 13% higher rate of new atrial fibrillation if they had no heart disease and a lower rate of progression if they did, with no dose recorded.¹¹ It fits the dose-related picture above; why is fish oil no longer recommended sets out the trials behind the headline.

What vitamins should not be taken with omega-3?

None, as far as trials can tell. Vitamin D and fish oil were given together to 25,871 adults for five years in the VITAL trial.¹² Signs of vitamin D deficiency covers the vitamin D side. Vitamin C, folic acid, iron and magnesium have no documented interaction with omega-3.

What are the side effects of taking omega-3?

A fishy aftertaste, burps, mild nausea and loose stools, more often at 2 to 4 g a day than at 1 g or less, and for a few an itchy rash; no serious adverse event was attributable to omega-3 across 21 prescription-dose trials in 24,460 people.¹³ The prescription-dose trials recorded a small rise in fasting blood sugar, but across 83 trials omega-3 changed neither HbA1c nor the rate of new diabetes.^{13, 20} What are the side effects of omega-3, 6 and 9 sets each effect against its dose; the Wellgard omega-3 guide covers the family.

Who should not take cod liver oil capsules?

Anyone pregnant or trying for a baby, unless a GP advises otherwise, because fish liver oils are high in vitamin A (retinol), which can harm an unborn baby.³ Fish body oil, krill oil, algal oil and flaxseed oil contain no vitamin A.

How do you know an omega-3 oil is good quality?

Freshness. Omega-3 oils oxidise in air, heat and light, and a survey of 171 shop-bought omega-3 products found half over the voluntary oxidation limits; oxidised oil tastes rancid, which is the usual cause of fishy burps.¹⁴ Keep capsules sealed, cool and out of sunlight.

What we don't know

No trial has tested omega-3 alongside a DOAC specifically; the bleeding data come from surgical patients and healthy volunteers.^{1, 5} The atrial fibrillation analysis excluded trials in people who already had the condition, so whether a label dose matters for them is untested.² The oxidation survey was North American; no UK survey of shop-bought capsules has been published.¹⁴

Frequently asked questions

When should you not take omega-3?

Without telling your GP or clinic if you take an anticoagulant or antiplatelet medicine; above 1 g a day without a doctor's reason; as cod liver oil in pregnancy; as fish oil with a fish allergy.^{1, 2, 3}

What is the downside of taking omega-3 fish oil?

The taste and the burps, and at doses above 1 g a day the atrial fibrillation signal.^{2, 13} At label doses, none documented for most adults.

Is too much omega-3 ALA bad?

No upper limit has been set for ALA, the plant omega-3 in flaxseed, chia and walnuts; the atrial fibrillation and bleeding findings concern EPA and DHA, and in the Cochrane review ALA trials showed no harm.¹⁵

Is too much omega-3 bad during pregnancy?

Across 70 trials of omega-3 in pregnancy, early preterm birth fell from 4.6% to 2.7%, with more pregnancies running past 42 weeks (2.6% against 1.6%) the one unwanted effect.⁷ The caution is vitamin A in fish liver oil; tell your midwife what you take.

Can I take ginkgo biloba and fish oil together?

No trial has tested the two together. Standardised ginkgo extract, in 18 randomised trials of 1,985 adults, did not change platelet clumping, fibrinogen or clotting times, and fish oil did not increase bleeding or transfusions across 52 studies.^{17, 1} If you take warfarin, a DOAC or an antiplatelet medicine, tell your GP or anticoagulant clinic about both, and the NHS says to check with a pharmacist before taking a herbal medicine alongside other medicines.¹⁸ What ginkgo biloba is good for has ginkgo's own trials.

Sources

1. Begtrup KM, et al. No impact of fish oil supplements on bleeding risk. Danish Medical Journal, 2017. Systematic review, 52 publications; funding not stated on PubMed. PubMed 28552094.
2. Gencer B, et al. Marine omega-3 supplementation and the risk of atrial fibrillation. Circulation, 2021. Meta-analysis, 7 trials, 81,210 people, 4.9 years; publicly funded (NIH). PubMed 34612056.
3. NHS. Fish and shellfish. Page last reviewed 26 June 2026. nhs.uk.
4. Albert CM, et al. Marine omega-3 and vitamin D supplementation and incident atrial fibrillation (VITAL Rhythm). JAMA, 2021. Randomised trial, 25,119 adults, median 5.3 years; publicly funded (NIH). PubMed 33724323.
5. Akintoye E, et al. Fish oil and perioperative bleeding. Circulation: Cardiovascular Quality and Outcomes, 2018. Randomised trial, 1,516 cardiac-surgery patients; funding not stated on PubMed. PubMed 30571332.
6. Arterburn LM, et al. Algal-oil capsules and cooked salmon: nutritionally equivalent sources of DHA. Journal of the American Dietetic Association, 2008. Randomised open-label trial, 32 adults, 2 weeks; manufacturer-funded. PubMed 18589030.
7. Middleton P, et al. Omega-3 fatty acid addition during pregnancy. Cochrane Database of Systematic Reviews, 2018. Cochrane review, 70 trials, 19,927 women; non-commercial funding. PubMed 30480773.
8. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register. Page last updated 19 May 2026. gov.uk.
9. Bhatt DL, et al. Cardiovascular risk reduction with icosapent ethyl for hypertriglyceridemia (REDUCE-IT). New England Journal of Medicine, 2019. Randomised trial, 8,179 statin-treated patients, median 4.9 years; manufacturer-funded. PubMed 30415628.
10. NHS. Warfarin. Page last reviewed 24 February 2026. nhs.uk.
11. Chen G, et al. Regular use of fish oil supplements and course of cardiovascular diseases. BMJ Medicine, 2024. Prospective cohort, 415,737 UK Biobank participants, median 11.9 years; charity-funded (Gates Foundation). PubMed 38800667.
12. Manson JE, et al. Marine n-3 fatty acids and prevention of cardiovascular disease and cancer (VITAL). New England Journal of Medicine, 2019. Randomised trial, 25,871 adults, median 5.3 years; publicly funded (NIH). PubMed 30415637.
13. Chang CH, et al. Safety and tolerability of prescription omega-3 fatty acids. Prostaglandins, Leukotrienes and Essential Fatty Acids, 2018. Meta-analysis, 21 trials, 24,460 people; funding not stated on PubMed. PubMed 29482765.
14. Jackowski SA, et al. Oxidation levels of over-the-counter omega-3 supplements. Journal of Nutritional Science, 2015. Product survey, 171 supplements; funding not stated on PubMed. PubMed 26688721.
15. Abdelhamid AS, et al. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews, 2020. Cochrane review, 86 trials, 162,796 people; non-commercial funding. PubMed 32114706.
16. European Food Safety Authority. EFSA assesses safety of long-chain omega-3 fatty acids. Published 27 July 2012. efsa.europa.eu.
17. Kellermann AJ, Kloft C. Bleeding risk with standardised Ginkgo biloba extract. Pharmacotherapy, 2011. Meta-analysis, 18 randomised trials, 1,985 adults; funding not stated on PubMed. PubMed 21923430.
18. NHS. Herbal medicines. Page last reviewed 1 May 2026. nhs.uk.
19. Retained Regulation (EU) No 1169/2011, Annex II: allergens to be declared, including crustaceans and fish. Latest available version. legislation.gov.uk.
20. Brown TJ, et al. Polyunsaturated fat and type 2 diabetes. BMJ, 2019. Meta-analysis, 83 trials of 24 weeks or longer; publicly funded (WHO). PubMed 31434641.

Spotted something out of date? Email support@wellgard.co.uk with the page address and the sentence.

This article is general information, not medical advice. If you take an anticoagulant or antiplatelet medicine, have a heart rhythm disorder, are pregnant or have surgery planned, speak to your GP or clinic first.