What is omega-3? A plain-English guide

Omega-3s are a family of fats that people get from food [1]. The two main long-chain forms are EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), which come from oily fish [1]. A third form, ALA (alpha-linolenic acid), comes from plants [1].

EFSA, the European Food Safety Authority, lists fish, fish oils, milk and farmed sea algae as food sources [10]. It says adults in the EU eat on average up to 400 to 500 mg a day from food [10].

The body can turn some plant ALA into EPA, but a review found this is limited in men [2]. Very little goes on to become DHA [2]. Women turn more ALA into these longer forms than men do [2].

The authors of one large review say many older adults take omega-3 hoping to keep their thinking sharp [3]. Researchers have studied omega-3 for overall thinking skills [3][4], for memory [4][5] and for blood triglycerides [1].

Does omega-3 help overall thinking skills?

Evidence grade for global cognition: N, no benefit shown. Why this grade

Reviews of trials found no clear effect. A meta-analysis is a study that pools the results of many trials. One meta-analysis pooled 25 randomized controlled trials, which are studies where people are split by chance into groups [4]. The adults in it did not have dementia, and some had mild cognitive impairment, a milder problem with memory and thinking [4]. It found no effect on overall thinking skills [4].

A larger meta-analysis pooled 38 trials with 49,757 adults, who were mostly older [3]. It found that EPA and DHA probably have little or no effect on new memory and thinking problems [3]. The World Health Organization paid for that review [3].

Single trials in healthy adults are mixed. In a 6-month trial in 193 healthy adults aged 20 to 80, 2.5 g a day did not improve test scores [6]. That trial compared omega-3 with a placebo, a dummy pill [6]. Our full research summary also covers a trial with a different result. A company that sells omega-3 ingredients paid for it.

Does omega-3 help memory?

Evidence grade for memory: C, limited. Why this grade

The evidence is mixed. The 25-trial meta-analysis found a mild benefit for memory [4]. Its authors said this benefit applied to older adults without dementia [4].

An earlier meta-analysis pooled 10 placebo-controlled trials [5]. It found no effect on overall memory scores [5]. That review included healthy adults, people with milder memory and thinking problems, and people with Alzheimer's disease [5].

The two reviews pooled different trials and different groups of people [4][5].

Does omega-3 lower blood triglycerides?

Evidence grade for blood triglycerides: A, strong. Why this grade

In trials, yes. A Cochrane review pooled 86 randomized trials with 162,796 people, and each trial lasted at least 12 months [1]. Getting more EPA and DHA lowered triglycerides by about 15% [1]. The effect grew as the dose went up [1].

The reviewers rated this finding as high-certainty evidence [1]. People in these trials had a range of heart risk, so they were not all healthy adults [1]. The UK Medical Research Council paid for the review [1].

To learn what each grade means, see how we grade evidence.

Table: Doses used in studies (not a recommendation)

These are amounts used in research, not advice for any reader. In 2012, EFSA found that extra EPA and DHA of up to 5 g a day combined raised no safety concerns for adults [10]. It said the data were not enough to set an upper limit [10]. A 2021 analysis of heart trials linked omega-3 supplements to a higher risk of atrial fibrillation, more so above 1 g a day [8]. Talk to a clinician about your own situation.

A meta-analysis of 90 trials looked at side effects [7]. People taking omega-3 had higher odds of diarrhea, changes in taste and a tendency to bleed than people on a placebo [7]. The review found no report of serious side effects clearly caused by omega-3 [7]. The Cochrane review found little or no effect on serious side effects [1].

Sources differ on bleeding. Unlike the 90-trial review, EFSA found in 2012 that up to 5 g a day did not raise reported bleeding in adults [10].

One warning sign in the research is atrial fibrillation, a type of irregular heartbeat [8]. A meta-analysis pooled 7 heart trials with 81,210 adults, whose average age was 65 [8]. In those trials, supplements were linked to a higher risk [8]. The rise was larger in trials using more than 1 g a day than in trials using less [8]. Our full research summary covers a newer analysis that differs on lower doses.

The Cochrane review looked at a wider group of heart rhythm problems and found little or no effect [1]. The reviewers had low confidence in that result [1].

One case report describes a woman taking warfarin, a blood thinner [9]. A blood-clotting test result rose after she doubled her fish oil from 1000 to 2000 mg a day [9]. It fell again after she cut back [9]. A single case cannot show that the fish oil caused the change. Our full research summary covers other warfarin studies.

The research points to two groups:

• Adults like those in heart trials (average age 65). In one analysis, the risk rose in both dose groups, more so above 1 g a day [8].
• People who take a blood thinner, such as warfarin. One case report links a rise in a blood-clotting test to a higher fish oil dose [9].

As of November 12, 2026, the sources we checked do not name pregnancy, breastfeeding or children as groups who should avoid or limit omega-3 supplements. They are the reviews cited here, EFSA and an archived copy of the NIH Office of Dietary Supplements fact sheet.

If you take a blood thinner, such as warfarin, talk to your doctor or pharmacist before combining it with omega-3.