Omega-3 supplements, usually fish oil or algae-derived oil, are among the most widely taken supplements and are generally well tolerated. Most side effects are mild and related to the oil itself rather than to any active effect.
Common side effects reported with this supplement or ingredient
- A fishy aftertaste, or fishy burps
- Nausea or indigestion
- Loose stools or diarrhoea, more likely at higher amounts
- Reflux
- A fishy body odour in some people
Taking capsules with food, or keeping them in the fridge, reduces the aftertaste for many people. Enteric-coated products are designed for the same problem.
Possible interactions with medicines, chronic conditions or pregnancy
Bleeding risk. Tell your doctor or pharmacist before taking this alongside warfarin, clopidogrel, aspirin or other blood thinners, and stop before planned surgery or dental procedures with the timing your clinician advises. See supplements and blood thinners and supplements before surgery.
At ordinary supplement amounts, the bleeding effect is modest and often clinically unimportant. It matters more at high doses and in combination with other things that thin the blood, including aspirin, anti-inflammatories, and other supplements such as turmeric, garlic, ginkgo and vitamin E. See fish oil and bleeding risk.
Other points to check: high doses have been associated with atrial fibrillation in some studies, so mention omega-3 if you have a heart rhythm condition. Fish allergy is a consideration, though the allergenic proteins are largely removed in processing; algae-based products avoid the question entirely. Omega-3 is often recommended in pregnancy, but choose a product appropriate for it, as some fish liver oils contain vitamin A at amounts not suitable in pregnancy.
Who should speak to a healthcare professional before using it?
Ask first if you take blood thinners, have a bleeding disorder, have a heart rhythm condition, have surgery planned, or are pregnant and unsure which product is suitable.
Dose, product-quality and stacking risks
Supplements in South Africa are regulated as complementary medicines, and the checks applied are not the same as those for prescription medicines. Strength, purity and labelling vary between products, and herbal products in particular can differ substantially in how much active compound they contain. See how supplements are regulated in South Africa and how to check supplement labels.
Stacking is a common problem: several products each containing the same ingredient add up to more than intended. See taking too many supplements.
Two quality issues are specific to fish oils. First, the label figure is often the total oil rather than the amount of active EPA and DHA, which can differ considerably between products at the same stated dose. Second, fish oils oxidise over time, and a rancid product is both less useful and more likely to cause digestive upset. Check expiry dates, store as directed, and treat a strongly rancid smell as a reason to discard rather than persist.
When to stop and get medical advice
Stop and seek advice for unusual bruising, bleeding that is slow to stop, blood in the urine or stools, or a new irregular heartbeat. Stop before planned surgery with the timing your clinician advises.
Related supplement safety guides
- Supplement side effects
- Supplement and medicine interactions
- Herbal supplement side effects
- When to see a doctor about a supplement
- Report a supplement side effect in South Africa
See also fish oil side effects.
Medical Disclaimer: This content is for informational and educational purposes only and does not constitute medical diagnosis, prescription, or professional advice. Always read the patient information leaflet and consult a qualified doctor or pharmacist regarding any medicine or health concern.