Omega-3 Side Effects: How Much Is Too Much and What You Should Know

In usual amounts, omega-3 is well tolerated, and the side effects that do occur are mostly harmless. Burps that taste of fish, a rumbling stomach, and with larger amounts sometimes loose stools. We're always talking about EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) from fish or algae here. Two things deserve to be taken more seriously: a slightly higher risk of atrial fibrillation that grows with the amount, and coordination with blood thinners. In Germany, the upper line that applies is the one from Germany's Federal Institute for Risk Assessment (BfR): no more than 1.5 g of EPA and DHA a day, from food and supplements combined.

You'll read plenty of warnings about this. How many people in the studies were actually affected, and at what amounts, is rarely mentioned, though. Here you'll find the numbers, including the ones that concern our own omega-3. What omega-3 is good for in the first place is explained in our omega-3 guide.

What are the side effects of omega-3?

How often your stomach and gut speak up is mainly a question of the amount. Two large studies show this. In VITAL, a US study with almost 26,000 adults aged 50 and over, half of the participants took 840 mg of EPA and DHA every day for a little over five years. Stomach and gut complaints were no more common than with a placebo. In the STRENGTH study with just over 13,000 high-risk patients, on the other hand, people got 4 g a day as a prescription drug. There, about one in four had stomach and gut complaints, compared with about one in seven on the corn oil used for comparison. And the high amount didn't give the patients any benefit for the heart at all.

How do you get rid of fishy burps and aftertaste?

Take omega-3 in the middle of a meal with some fat, not on an empty stomach. That's also what our own intake recommendation says, for the best possible tolerability. More on this in taking omega-3 with food. With algae oil you lose the fishy taste completely, because it delivers the same fatty acids straight from the microalgae. What else makes the difference for freshness and smell is in our comparison of algae oil and fish oil.

How much omega-3 is too much?

There's no legal maximum, but there are two reference values. By the more cautious one, from the BfR, it's too much if you regularly take in more than 1.5 g of EPA and DHA a day from all sources combined.

In its 2012 safety assessment, the European Food Safety Authority (EFSA) deliberately didn't set a fixed upper limit, because the data aren't sufficient for one. It does, however, see no safety concerns for adults with supplemental amounts of up to 5 g of EPA and DHA a day, up to 1.8 g for EPA alone and up to about 1 g for DHA alone. The BfR drew its line in 2009 and confirmed it in its questions and answers on omega-3 from April 2026. It isn't a law. But because it's the stricter of the two, it's the one we work with here.

On cholesterol, the two authorities part ways. This is about LDL cholesterol, the blood lipid value that usually gets measured at a checkup. In its 2009 opinion, the BfR named as a possible risk an "increase in LDL cholesterol levels from 0.7 g of DHA/EPA per day". EFSA came to a milder view in 2012: at 2 to 6 g a day, LDL cholesterol rose by about 3%, which in its assessment is unlikely to have an adverse effect on cardiovascular risk.

Whether you need more is shown by the omega-3 index, and how much is right for you, we work out in getting your omega-3 dosage right.

The authorized health claims are also about amounts. The claim that EPA and DHA contribute to the normal function of the heart is authorized at 250 mg a day. That's the amount EFSA considers adequate in its reference values for fats. The claims on blood pressure and blood triglyceride levels require 3 g and 2 g respectively. And anyone advertising with those must, under EU rules, add that a total of 5 g a day should not be exceeded. There's no authorized claim on heart rhythm, cholesterol or blood clotting, only studies.

Does omega-3 increase the risk of atrial fibrillation?

Slightly, yes, and it depends on the amount: in an analysis of large studies, atrial fibrillation occurred 12% more often in relative terms with up to 1 g of omega-3 a day, and 49% more often with more than 1 g.

Atrial fibrillation is a heart rhythm disorder in which the upper chambers of the heart beat irregularly and usually too fast. The analysis of seven large heart studies with just over 81,000 participants pooled over about five years what those studies had often only counted on the side. Patients and healthy people were mixed together, and the increase already showed up below 1 g.

What that means in real numbers is shown by the VITAL rhythm study. Just over 25,000 adults without heart disease took 840 mg of EPA and DHA a day or a placebo for a little over five years. Out of every 1,000 people, 37 developed atrial fibrillation during that time with omega-3 and 34 without. This difference was not statistically significant. If you apply the 12% from the large analysis to this starting point, you end up with roughly four additional cases per 1,000 people over five years. That's the order of magnitude you can use to put the warnings into perspective.

In 2023 the BfR pointed out this risk in heart patients. It rose with the dose and was greatest at 4 g a day. In its questions and answers, the BfR puts this at supplemental amounts from about 1.8 g a day over a longer period. It advises people with heart disease or corresponding risk factors to take such supplements "only after consulting a doctor, especially over a longer period". More on the heart studies is in VITAL, REDUCE-IT and other heart studies.

Does omega-3 thin your blood?

A little, but it doesn't make bleeding more common. What can be measured is that the platelets clump together slightly less easily. A Danish review of 52 papers saw this in healthy people, and in 2009 the BfR also mentioned "indications of an increased bleeding tendency from 1.5 g of DHA/EPA per day". Newer data, however, give a pretty clear all-clear. In an analysis of eleven large studies with over 120,000 people, bleeding occurred in 2.6% with omega-3 and in 2.4% without. That's within the range of chance, and that also held for those who were additionally taking drugs against platelet clumping. A small increase only showed up with prescription drugs made from high-dose pure EPA.

Can you take omega-3 with blood thinners and other medications?

Blood thinners are where the interaction that really matters with omega-3 lies. That's why omega-3 always belongs in the conversation with your doctor in that case. This has mainly been studied for warfarin, which belongs to the same group as Marcumar (phenprocoumon), the drug commonly used in Germany. In an analysis of 573 patients on warfarin, clotting values stayed stable on average with fish or krill oil, and bleeding was no more common. In one reported individual case, however, the clotting value, called INR in practice, rose clearly after someone had doubled their fish oil intake from 1,000 to 2,000 mg.

Nothing can be concluded from these data for the newer blood thinners, so with any anticoagulant you check omega-3 and every later change in the amount with your doctor first. For other long-term medications, just ask briefly at your pharmacy.

Who should talk to a doctor before taking omega-3?

Talk to your doctor first if any of these points apply to you:

• You have a heart rhythm disorder, another heart condition or risk factors for one.
• You take anticoagulants such as Marcumar or warfarin.
• You're pregnant or breastfeeding. Then it's less about too much and more about the right amount, because the BfR explicitly recommends DHA for pregnant and breastfeeding women who don't eat fish, after advice from their gynecologist.
• It's about a child or a teenager.

These life stages come with their own, lower amounts. For pregnant women, Germany's Healthy Start network (Netzwerk Gesund ins Leben) gives 200 mg of DHA a day. And according to their EU authorization as a novel food, supplements with algae oil from the microalga Schizochytrium may provide no more than 450 mg of EPA and DHA a day for pregnant and breastfeeding women, and no more than 250 mg for children from 18 months and teenagers. More on this in omega-3 in pregnancy, breastfeeding and menopause. For children, the pediatrician is the right person to ask.

Where does PULSE stand relative to these limits?

Two Liquid-Caps of PULSE by Fifty Five provide 648 mg of EPA and DHA a day, 432 mg of which is DHA. That's a long way from high amounts: it's an eighth of the 5 g from the EFSA assessment, and the 432 mg of DHA is well below the 1 g EFSA sets for DHA alone.

If you add what comes in on average from food, you end up at 775 to 943 mg a day. That's clearly below the BfR line of 1.5 g. It only gets tight if you also eat two or more servings of oily sea fish like salmon or mackerel a week, and PULSE isn't meant for that case anyway, but for everyone who rarely or never eats fish. And as with any other omega-3 supplement: if you have heart rhythm problems or take blood thinners, talk to your doctor first.

FAQ

Is algae oil well tolerated?

Yes. What matters most for tolerability is the amount of EPA and DHA, and the BfR line explicitly applies regardless of whether the fatty acids come from fish oil, algae oil or as ethyl esters. In the EU, algae oil from Schizochytrium is also only authorized with strict freshness requirements. These include a peroxide value of no more than 5, a measure of how far an oil has already oxidized. And without fish, the fishy aftertaste is gone, for many people the most common reason to drop omega-3 again after a few weeks. That's exactly how it went for Sophia with her fish oil capsules.

Can omega-3 cause diarrhea?

Yes, especially in large amounts. Stomach and gut complaints increase with the amount, and loose stools are among the typical ones. So take omega-3 with a main meal. If the diarrhea continues even after a break, have it checked by a doctor.

Is omega-3 bad for your liver?

The studies and official assessments we rely on here contain no solid data on this. EFSA sees no safety concerns with supplemental amounts of up to 5 g a day, but doesn't specifically mention the liver. If you have a liver condition, it's best to discuss food supplements with your doctor beforehand.

Do I need to stop taking omega-3 before surgery?

According to the evidence, not necessarily. The Danish review of 52 papers found neither more blood loss nor more blood transfusions in surgical patients and saw no reason to stop fish oil beforehand. Still, let your surgical team know, especially if you're also getting blood thinners.

Can you take omega-3 every day?

Yes, and that actually makes sense. EPA and DHA are built into the membranes of your cells, and those renew themselves only slowly, over months. That's why it counts that a little more arrives every day. With a usual daily amount, you stay clearly below the EFSA and BfR lines in the long run too.

Disclaimer:

This article is for informational purposes only and does not replace medical advice, diagnosis, or treatment by a physician or pharmacist. The information provided here should not be used for self-diagnosis or self-treatment. Food supplements are no substitute for a balanced, varied diet and a healthy lifestyle. For any health questions or complaints, please always consult a doctor you trust. Fifty Five accepts no liability for any inconvenience or harm resulting from the use of the information presented here.

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