Omega-3 fatty acids are a group of polyunsaturated fatty acids. The best known are EPA (eicosapentaenoic acid) and DHA ( docosahexaenoic acid ), which are found mainly in fatty fish, fish oil, and algae oil, and ALA (alpha-linolenic acid), which is found in flaxseed and walnuts, among other things. Omega-3 supplements are generally well tolerated. However, some people may experience mild side effects, especially at the beginning. In this article, you will read what these symptoms are, when they occur, and what you can do about them.
This article provides general information and does not replace personal medical advice.
Safety in a nutshell
The European Food Safety Authority (EFSA) concluded that an intake of up to 5 g of EPA and DHA combined per day poses no safety risk for adults [1]. This is well above what a common dietary supplement provides. The side effects that do occur are usually mild and strongly correlated with the dose.
The most common side effects
The complaints that are reported most often are [2]:
• a fishy aftertaste or breath
• belching or burping
• heartburn or stomach discomfort
• nausea
• loose stools or diarrhea
The frequency of these complaints depends mainly on the amount. In a large study with a high dose of 4 g omega 3 per day, 11.9% of participants experienced diarrhea, compared to 4.9% in the placebo group [3]. In a study with more than 18,000 participants who took 1 g per day for years, stomach complaints occurred as often as with placebo [4].
When do side effects occur?
Within a few minutes to hours after ingestion. A fishy aftertaste and belching usually occur shortly after ingestion, especially if the oil is already released in the stomach.
In the first days to weeks. Nausea, stomach upset, or loose stools occur especially when you are just starting, switching products, increasing the dose, or taking omega-3 on an empty stomach.
Six practical tips to reduce symptoms
1. Take omega-3 at (the beginning of) a meal. Fat in your meal kickstarts the digestion of fats. As a result, EPA and DHA are better absorbed: in research, absorption increased up to threefold with a higher-fat meal [5]. Furthermore, the oil remains undigested in your stomach for a shorter time.
2. Divide the intake throughout the day. Two smaller portions are often better tolerated than one large one.
3. Choose a different time. If you are prone to burping or heartburn in the evening, do not take omega-3 right before going to bed.
4. Check the shelf life and storage. Oxidized oil has a stronger smell and taste. Store your supplement in a cool, dark, and tightly sealed place, and observe the expiration date.
5. Try a different form. Capsules are taste-neutral but may cause burping. Equazen Jelly or Equazen Forte contain technologies that prevent this. Liquid oil, such as in Equazen Liquid, is easier to taste but is easy to combine with food.
6. Consider algae oil. EPA and DHA from microalgae are absorbed just as well as from fish [6] and do not contain fish, which can limit a fishy aftertaste. The only downside: EPA is still difficult to produce in high concentrations from algae. As a result, most algae oils contain mainly DHA and relatively little EPA. So check the label to see exactly how much EPA and how much DHA is in it.
When is it best to consult your doctor or pharmacist?
When using blood thinners. Omega-3 has a mild inhibitory effect on platelets. However, a large analysis of randomized studies involving more than 120,000 patients found no increase in bleeding, even in people who also used antiplatelet agents [7]. Only at very high doses of pure EPA was a small increase seen [7]. If you are taking a blood thinner such as warfarin, tell your doctor that you are taking omega-3, especially if you increase the dose.
In case of heart disease. In studies in people with cardiovascular disease or an increased risk thereof, omega-3 was associated with a slightly increased risk of atrial fibrillation, a heart rhythm disorder. That risk increases with the dose: the relative risk was about 12% higher at up to 1 g per day and about 49% higher above 1 g per day [8]. The Federal Agency for Medicines and Health Products (FAMHP) and the European Medicines Agency included this in the package leaflet for omega-3 medicines in 2023, with the highest risk at 4 g per day [9]. If you have a heart condition or a heart rhythm disorder, discuss omega-3 with your doctor beforehand.
During pregnancy and breastfeeding. Omega-3, and DHA in particular, is especially important during this period. EFSA advises pregnant and breastfeeding women to take an additional 100 to 200 mg of DHA on top of the standard recommendation of 250 mg of EPA and DHA per day [10]. Consult your doctor or midwife about which form and dose is right for you.
In case of a fish or shellfish allergy. Refined fish oil contains hardly any fish protein, and in a small study, people with a fish allergy tolerated fish oil supplements without a reaction [11]. However, a reaction cannot be completely ruled out. Therefore, consult your doctor beforehand, or choose algae oil.
In case of persistent symptoms. If your symptoms do not disappear, discuss them with your GP or pharmacist. Bring the packaging of your supplement with you so that it is clear exactly what and how much you are taking.
Frequently Asked Questions
Can omega-3 cause immediate side effects?
Yes. A fishy aftertaste and belching may occur shortly after ingestion. Gastrointestinal complaints are more likely to appear in the first few days or weeks.
Why do I burp from omega-3?
Belching is among the most frequently reported complaints. Taking it with a meal, spreading the dose, or trying a different form often helps.
Is a fishy aftertaste an allergic reaction?
No. An aftertaste is a taste and smell experience. An allergy is a reaction of the immune system, with, for example, a skin rash, itching, or swelling.
Should I stop if I feel nauseous?
Not necessarily. First, check if you are taking omega-3 on an empty stomach, if you have just started, or if you have switched products. Take it with a meal or divide the dose. If the nausea persists, consult your doctor or pharmacist.
Does the form or the source make a difference?
That is possible. Some people tolerate capsules better, others liquid oil. Algae oil is an alternative for those who are bothered by the fishy aftertaste or do not want to use fish.
What if my symptoms don't go away?
Discuss them with your GP or pharmacist and take the packaging with you.
Dietary supplements are not a substitute for a varied, balanced diet and a healthy lifestyle. In case of persistent symptoms, doubt, or if you are taking medication, consult your GP or pharmacist.
References
1. EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). 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
2. National Institutes of Health, Office of Dietary Supplements . Omega-3 Fatty Acids : Fact Sheet for Health Professionals [Internet]. Bethesda (MD): NIH ODS [accessed 23 Sep 2026]. Available at: https://ods.od.nih.gov/factsheets/Omega3FattyAcids-HealthProfessional/
3. Nicholls SJ, Lincoff AM, Garcia M, Bash D, Ballantyne CM, Barter PJ, et al. Effect of high-dose omega-3 fatty acids vs corn oil on major adverse cardiovascular events in patients at high cardiovascular risk: the STRENGTH randomized clinical trial. JAMA. 2020;324(22):2268-80. doi:10.1001/jama.2020.22258
4. Okereke OI, Vyas CM, Mischoulon D, Chang G, Cook NR, Weinberg A, et al. Effect of long-term supplementation with marine omega-3 fatty acids vs placebo on risk of depression or clinically relevant depressive symptoms and on change in mood scores: a randomized clinical trial. JAMA. 2021;326(23):2385-94. doi:10.1001/jama.2021.21187
5. Lawson LD, Hughes BG. Human absorption of fish oil fatty acids as triacylglycerols, free acids, or ethyl esters. Biochem Biophys Res Commun. 1988;152(1):328-35. doi:10.1016/s0006-291x(88)80718-6
6. Arterburn LM, Oken HA, Bailey Hall E, Hamersley J, Kuratko CN, Hoffman JP. Algal-oil capsules and cooked salmon: nutritionally equivalent sources of docosahexaenoic acid. J Am Diet Assoc. 2008;108(7):1204-9. doi:10.1016/j.jada.2008.04.020
7. Javaid M, Kadhim K, Bawamia B, Cartlidge T, Farag M, Alkhalil M. Bleeding risk in patients receiving omega-3 polyunsaturated fatty acids: a systematic review and meta-analysis of randomized clinical trials. J Am Heart Assoc. 2024;13(10):e032390. doi:10.1161/JAHA.123.032390
8. Gencer B, Djousse L, Al-Ramady OT, Cook NR, Manson JE, Albert CM. Effect of long-term marine ω-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):1981-90. doi:10.1161/CIRCULATIONAHA.121.055654
9. Federal Agency for Medicines and Health Products (FAMHP). PRAC October 2023: new safety information for omega-3 acid ethyl esters [Internet]. Brussels: FAMHP; 12 Oct 2023 [accessed 23 Sep 2026]. Available at: https://www.famhp.be/en/news/prac_october_2023_new_safety_information_for_omega_3_acid_ethyl_esters
10. EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). 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
11. Mark BJ, Beaty AD, Slavin RG. Are fish oil supplements safe in finned fish-allergic patients? Allergy Asthma Proc. 2008;29(5):528-9. doi:10.2500/aap.2008.29.3159