Who should not take fish oil?

The short answer

Fish oil is safe for most adults at normal doses. Check with a doctor before you start if any of these apply:

  • You take blood thinners or antiplatelet drugs, or have a bleeding disorder.
  • You have atrial fibrillation or a history of it, and plan to take more than 1 g a day.2
  • You're allergic to fish or shellfish.
  • You have surgery coming up, or take blood pressure medicine.

Almost all of the real risks come down to two things: fish oil's mild effect on blood clotting and blood pressure, and the dose. At the 250 mg to 1 g of EPA+DHA a day most people take, problems are rare. At 3–4 g a day, the doses used for triglycerides and arthritis, the list of people who should be supervised gets longer.

On this page

Who should check with a doctor before taking fish oil?

If you…Why it mattersWhat to do
Take blood thinnersOmega-3s slightly reduce platelet stickiness, which adds to the effect of anticoagulant and antiplatelet drugs.Ask your doctor. On warfarin, they may want to check your INR after you start.
Have a bleeding disorderAny extra effect on clotting matters more when clotting is already impaired.Don't start without your haematologist's agreement.
Have atrial fibrillationIn heart-outcome trials, doses above 1 g a day were linked to a higher risk of atrial fibrillation.2Agree any dose with your cardiologist, especially above 1 g a day.
Are allergic to fish or shellfishPurified fish oil contains very little protein, but reactions are possible and krill oil comes from shellfish.Ask an allergist. Algal oil avoids fish and shellfish entirely.
Take blood pressure medicineEPA+DHA lowers blood pressure a little: about 4.5 mmHg systolic in untreated high blood pressure.4Usually fine. Mention it to your doctor and keep checking your BP.
Have surgery coming upMany surgeons ask you to stop, although a large trial found no extra bleeding (see below).1Follow your surgeon's instructions.
Are pregnant or breastfeedingDHA is beneficial in pregnancy. The risk is cod liver oil, whose vitamin A can be harmful at high intakes.Fish oil or algal DHA is fine. Avoid cod liver oil, and agree high doses with your obstetrician.
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The bleeding risk is smaller than people think

In a trial of 1,516 heart surgery patients, people given 8–10 g of EPA+DHA in the days before surgery and 2 g a day afterwards had no more major bleeding than those given placebo, and they needed fewer blood transfusions.1 That's reassuring, but it isn't a reason to ignore your doctor if you're on anticoagulants.

What should you not mix omega-3 with?

No common medicine is strictly forbidden with fish oil. These are the combinations worth clearing with a doctor or pharmacist first:

  • Anticoagulants and antiplatelets: warfarin, apixaban, rivaroxaban, dabigatran, clopidogrel, ticagrelor and daily aspirin. The effects on clotting add up.
  • Other supplements that thin the blood: ginkgo, high-dose garlic, high-dose vitamin E and curcumin. One of these with fish oil is usually fine. Several at high doses, on top of a blood thinner, is not a good idea.
  • Blood pressure medicines: the effects add up, but the extra drop is small.4
  • Other vitamin A or D supplements, if you use cod liver oil: cod liver oil already contains both, and stacking it with a multivitamin can push vitamin A too high.

There's no need to separate fish oil from most other supplements or meals. In fact it's absorbed best with food. Our omega-3 FAQ explains timing.

Can I take omega-3 without a doctor?

Yes, if you're a healthy adult taking a normal dose. In India, fish oil capsules are sold as FSSAI-regulated health supplements, not as prescription medicines, so you can buy them over the counter. A daily dose of 250 mg to 1 g of EPA+DHA is a reasonable self-managed amount for general health.

Involve a doctor if you:

  • take any regular prescription medicine, especially for the heart, blood pressure or clotting
  • want to take more than 1–2 g a day, for example for high triglycerides or joint pain
  • are pregnant, breastfeeding, or buying for a child
  • have a heart rhythm problem, a bleeding problem, or liver disease

Is omega-3 safe for kids?

Yes, from food and at child-appropriate doses. The European Food Safety Authority advises that children over two follow the same guidance as adults, which works out to one to two portions of oily fish a week. For babies aged 6–24 months, it sets an adequate intake of 100 mg of DHA a day.5

If your child doesn't eat fish, a children's DHA or fish oil product is reasonable. Three things to watch:

  • Use a product made for their age, not adult triple-strength capsules, and follow its dose.
  • Avoid cod liver oil if they already take a multivitamin. The vitamin A adds up.
  • Gummies often contain little EPA+DHA and a lot of sugar. Check the label for mg of EPA and DHA.

Don't expect omega-3 to fix attention or school performance. A Cochrane review of omega-3 for ADHD found little evidence of benefit.6 For vegetarian families, algal DHA is the only plant source of real DHA. See our omega-3 comparison for options.

Fish oil side effects, and how to avoid them

Side effectHow commonWhat helps
Fishy burps, aftertasteCommonTake with your largest meal, refrigerate the bottle, try enteric-coated capsules. Strong rancid burps mean the oil has oxidised: replace it.
Indigestion, nauseaCommon at higher dosesTake with food and split the dose across two meals.
Loose stoolsOccasional, dose-relatedLower the dose, then build up slowly.
Easy bruising, nosebleedsUncommonStop and see a doctor, especially if you take blood thinners.
Atrial fibrillationSmall extra risk above 1 g/day2Keep to 1 g/day or less unless a doctor advises more. Report palpitations.

How much fish oil is too much?

EFSA considers up to 5 g of EPA+DHA a day safe for healthy adults.3 That's far more than most people need: 250–500 mg a day covers general health guidelines. The more practical limit is the atrial fibrillation signal. A meta-analysis of heart-outcome trials found doses above 1 g a day were linked to a higher risk.2 So the rule of thumb:

  • Up to 1 g EPA+DHA a day: fine for most healthy adults without medical advice.
  • 1–3 g a day: reasonable for specific goals, but tell your doctor.
  • Above 3 g a day: only with medical supervision.

Remember to count EPA+DHA, not fish oil. A "1000 mg fish oil" capsule usually contains about 300 mg of EPA+DHA.

Fish oil safety: FAQ

Who should not take fish oil?

Check with a doctor before taking fish oil if you take blood thinners or antiplatelet drugs, have a bleeding disorder, have atrial fibrillation or a history of it, are allergic to fish or shellfish, take blood pressure medicine, or have surgery coming up. For most other healthy adults, 250 mg to 1 g of EPA+DHA a day is safe without medical advice.

What should you not mix omega-3 with?

Be careful combining fish oil with blood thinners (warfarin, apixaban, rivaroxaban, clopidogrel, daily aspirin), with other supplements that can thin the blood (ginkgo, high-dose garlic, high-dose vitamin E, curcumin), and with blood pressure medicines. Don't stack cod liver oil with other vitamin A or D supplements. None of these is an absolute ban, but they're worth clearing with your doctor.

Can I take omega-3 without a doctor?

Yes, if you're a healthy adult taking a normal dose. Fish oil is sold in India as an FSSAI-regulated health supplement, not a prescription drug. Up to about 1 g of EPA+DHA a day is reasonable without medical advice. See a doctor first if you take regular medicines, have a heart rhythm or bleeding problem, are pregnant, or want to take more than 1–2 g a day.

Is omega-3 safe for kids?

Yes, in food and at child-appropriate doses. EFSA advises that children over two follow adult guidance of one to two portions of oily fish a week. If your child doesn't eat fish, a children's DHA or fish oil product is reasonable, but use one made for their age rather than adult capsules, and avoid cod liver oil if they already take a multivitamin with vitamin A. Evidence that omega-3 improves ADHD or school performance is weak.

What are the side effects of fish oil?

The common ones are fishy burps, an aftertaste, indigestion, nausea and loose stools. Taking it with your largest meal, splitting the dose, keeping the bottle in the fridge and choosing enteric-coated capsules all help. Above 1 g a day there is a small increase in the risk of atrial fibrillation in people with heart risk factors.

How much fish oil is too much?

EFSA considers up to 5 g of EPA+DHA a day safe for healthy adults. Most people need 250–500 mg a day for general health. Doses above 1 g a day have been linked to a higher atrial fibrillation risk, so anything above 1–2 g a day should be agreed with a doctor, especially if you have heart disease.

Should I stop fish oil before surgery?

Ask your surgeon; many still advise stopping 1–2 weeks before. The evidence is reassuring: in a trial of 1,516 heart surgery patients, high-dose fish oil before and after the operation did not increase major bleeding and reduced the number of blood transfusions. Follow your surgical team's instructions.

References

1
Akintoye E, Sethi P, Harris WS, et al. Fish oil and perioperative bleeding. Circ Cardiovasc Qual Outcomes. 2018;11(11):e004584. doi:10.1161/CIRCOUTCOMES.118.004584
2
Gencer B, Djousse L, Al-Ramady OT, et al. Effect of long-term marine omega-3 fatty acids supplementation on the risk of atrial fibrillation in randomized controlled trials of cardiovascular outcomes: a systematic review and meta-analysis. Circulation. 2021;144(25):1981–1990. doi:10.1161/CIRCULATIONAHA.121.055654
3
EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on the tolerable upper intake level of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA). EFSA J. 2012;10(7):2815. doi:10.2903/j.efsa.2012.2815
4
Miller PE, Van Elswyk M, Alexander DD. Long-chain omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid and blood pressure: a meta-analysis of randomized controlled trials. Am J Hypertens. 2014;27(7):885–896. doi:10.1093/ajh/hpu024
5
EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on dietary reference values for fats, including saturated fatty acids, polyunsaturated fatty acids, monounsaturated fatty acids, trans fatty acids, and cholesterol. EFSA J. 2010;8(3):1461. doi:10.2903/j.efsa.2010.1461
6
Gillies D, Sinn JK, Lad SS, Leach MJ, Ross MJ. Polyunsaturated fatty acids (PUFA) for attention deficit hyperactivity disorder (ADHD) in children and adolescents. Cochrane Database Syst Rev. 2012;(7):CD007986. doi:10.1002/14651858.CD007986.pub2

Not medical advice. This guide is general information about supplement safety, not a substitute for advice from your doctor or pharmacist. Don't stop or change prescribed medicine because of anything you read here.