Is omega-3 safe? Side effects and who should ask first
The common side effects of omega-3 supplements are usually mild. Large amounts can affect clotting, so if you take a blood thinner or any medicine regularly, ask your doctor first.
The omega-3 bottle is on the high shelf in your kitchen. You take it down to read the warnings before opening it.
What side effects should you watch for, and who should ask a doctor first?
Common side effects
The NIH (US National Institutes of Health) says the commonly reported side effects of omega-3 supplements are usually mild. They include an unpleasant taste, bad breath, heartburn, nausea, stomach upset, diarrhoea, headache and smelly sweat.[1]
This list is for omega-3 supplements in general, whatever the oil. If a side effect bothers you or does not go away, tell your doctor.
Blood thinners and bleeding
The NIH says omega-3 supplements such as fish oil can interact with medicines. It advises anyone who takes medicines regularly to discuss possible interactions with their health care provider.[1]
In large amounts, fish oil can make platelets, the parts of the blood that help it clot, clump together less. With one common blood thinner, fish oil might make blood take longer to clot.[1] Your doctor decides whether you take them together.
The Institute of Medicine is a US expert body. It noted that 2 to 15 g a day of the 2 omega-3s from fish and algae (EPA and DHA) might lengthen bleeding time.[1] If you take an omega-3 supplement, tell your surgeon or dentist.
If you have heart disease or a high risk of it, ask your doctor before starting a high-dose omega-3 supplement. In 2 large trials in these groups, taking 4 g a day for several years slightly raised the risk of atrial fibrillation, a type of irregular heartbeat.[1]
Do capsules contain mercury?
Seafood contains varying levels of methylmercury, a heavy metal. The NIH says omega-3 supplements have not been found to contain it, because processing and purification remove it.[1] The NIH's source for this is a 2016 review by a commercial testing company.
Children
For a child of any age, ask the child's doctor before you buy a supplement for them.
India's food safety regulator, FSSAI, has rules for health supplements and nutraceuticals, 2 kinds of supplement product. Some products under these rules are meant for children aged 2 to 5. These may be given only on the advice of a doctor, a certified dietitian or a nutritionist.[2] A nutraceutical pack must also say to store it out of reach of children.[2]
Each risk and what to do
| Who it applies to | What to do | |
|---|---|---|
| Common side effects | Anyone taking an omega-3 supplement | Usually mild. Tell your doctor if one bothers you or does not go away. |
| Bleeding with a blood thinner | People who take a blood thinner | Ask your doctor first. Your doctor decides whether you take them together. |
| Surgery or dental work | Anyone taking an omega-3 supplement | Tell your surgeon or dentist |
| Children | A child of any age | Ask the child's doctor before you buy a supplement for them |
What should you watch for when you take omega-3? Stomach upset and other side effects are usually mild. If you take medicines regularly, ask your doctor before you start. If you are pregnant, see omega-3 in pregnancy.
Ask your doctor before you take an omega-3 supplement if you take a blood thinner or any medicine regularly, are pregnant or breastfeeding, or are buying it for a child.
If you have a fish or shellfish allergy, ask your doctor before you take fish or krill oil.
Do not take more than the pack says.
Do not stop or cut down a medicine your doctor prescribed and take a supplement instead.
If you take a medicine for weight management, tell your doctor before you add a capsule.
Medical disclaimer: This article is general information. It does not replace advice from your doctor about your own health.
Common questions
The NIH says the common side effects are usually mild. They include an unpleasant taste, bad breath, heartburn, nausea, stomach upset, diarrhoea, headache and smelly sweat.
Ask your doctor first. In large amounts, fish oil can make platelets clump together less. The NIH advises anyone who takes medicines regularly to discuss possible interactions with their health care provider.
Sources
- National Institutes of Health, Office of Dietary Supplements. Omega-3 fatty acids: fact sheet for health professionals [Internet]. National Institutes of Health; 2025 Aug 22 [cited 2026 Oct 23]. Available from: ods.od.nih.govCited atSafety of Omega-3sInteractions with MedicationsInteractions with MedicationsSafety of Omega-3sSafety of Omega-3sSources of Omega-3s, Dietary supplements
- Food Safety and Standards Authority of India. Food Safety and Standards (Health Supplements, Nutraceuticals, Food for Special Dietary Use, Food for Special Medical Purpose, Functional Food and Novel Food) Regulations, 2016. New Delhi: FSSAI; 2021 Sep 29. Compendium Version-I. Available from: fssai.gov.inCited atReg 3(26), p. 6Reg 7(4)(iii)(i), pp. 13 to 14