Omega-3 (DHA and EPA)

Each outcome below is graded on its own. For how goals group these outcomes, see work and study, memory and healthy ageing.

Does omega-3 improve overall cognition in healthy adults?

The pooled analyses cited here find little or no effect. A meta-analysis of 25 randomized controlled trials in non-demented adults found no effect on global cognitive function, with an effect size (Hedges' g, a standardized difference between groups) of 0.02 [6]. A WHO-funded meta-analysis of 38 trials lasting at least 24 weeks (49,757 participants, mostly older adults) concluded that long-chain omega-3 probably has little or no effect on new cognitive impairment [4]. On the Mini-Mental State Examination it found a mean difference of 0.10 (95% CI 0.03-0.16) across 13 trials, which the authors counted as no or very little effect (moderate-quality evidence), with no differences by dose or duration [4].

The Cochrane review in cognitively healthy adults aged 60 and over reached the same conclusion: in two trials with 3221 participants there was no difference from placebo on the Mini-Mental State Examination after 24 or 40 months [5]. A meta-analysis of 24 trials in healthy people and in children with attention and related disorders found no improvement on any cognitive measure in the whole sample [7].

Individual trials in healthy adults of different ages were also null:

• In 159 healthy adults aged 18-35, 1 g a day of DHA-rich or EPA-rich fish oil for 12 weeks had minimal effects compared with placebo [10].
• In 193 healthy adults aged 20 to 80, 2.5 g a day for 6 months did not improve cognitive performance [11].
• In 390 cognitively healthy adults aged 65-90, 1720 mg DHA plus 600 mg EPA daily for 18 months did not maintain or improve cognitive performance compared with olive oil, and participants taking fish oil reported more cognitive mistakes [9].

Two newer dose-response meta-analyses point the same way. In 24 trials in 9,660 adults aged 40 and over without dementia, omega-3 was not associated with changes in global cognition or five other cognitive domains, though the authors reported a possible benefit for executive function [27]. A meta-analysis of 58 trials that mixed healthy people with people who had dementia or cognitive impairment reported better global cognition with higher doses (low-certainty evidence, with significant publication bias), but in its healthy subgroup the difference was not statistically significant [28].

The main exception is a 26-week trial in 310 healthy adults aged 25-49, funded by the omega-3 ingredient supplier BASF, in which an EPA-rich oil improved global accuracy and speed compared with placebo and with a DHA-rich oil [12].

Does omega-3 improve memory?

Evidence is mixed, and the positive findings come mostly from older adults with memory complaints. The 25-trial meta-analysis that found no global effect did find a mild benefit for memory (Hedges' g 0.31), and its authors limited that conclusion to non-demented older adults [6]. An earlier meta-analysis of 10 placebo-controlled trials that pooled healthy adults with people who had cognitive impairment or Alzheimer's disease found no effect on composite memory (g = 0.04) and no benefit for working memory [8].

A meta-analysis whose lead author was employed by DSM Nutritional Products, which sells omega-3 oils, and whose co-author was a paid DSM consultant, found that DHA with or without EPA improved episodic memory in adults with mild memory complaints [13]. In that same industry-linked analysis, doses above 1 g a day improved episodic memory regardless of baseline status, while semantic and working memory showed no between-group differences [13].

Individual trials:

• In 485 adults aged 55 and over whose memory scores were at least one standard deviation below younger adults, 900 mg of DHA a day for 24 weeks led to fewer errors than placebo on a visuospatial learning and episodic memory test but did not change working memory, in a trial whose first author was affiliated with the DHA supplier Martek Biosciences [14].
• In a small proof-of-concept trial in 44 cognitively healthy adults aged 50-75, 2,200 mg a day for 26 weeks improved recall of object locations but not performance on a verbal learning test [16].
• In 259 older adults with subjective or mild cognitive impairment (a clinical population), DHA-rich fish oil combined with cocoa flavanols for 12 months had no significant benefit on cognitive outcomes, and some measures declined compared with the control group, in a trial that listed Abbott Nutrition among its funders [17]. Results may not apply to healthy adults.

In younger adults who eat little DHA, the evidence comes mainly from one trial. In a 6-month randomized, placebo-controlled, double-blind trial in 176 healthy nonsmoking adults aged 18-45 with a low intake of DHA, 1.16 g of DHA a day sped up reaction times on episodic and working memory tasks compared with placebo [15]. Effects also differed by sex: DHA improved episodic memory in women (0.28 SD) and working-memory reaction time in men (-0.60 SD) [15].

A meta-analysis of trials in adults and school-aged children found that, in those with low omega-3 status, supplementation improved short-term memory, and its authors called the evidence in deficient people marginal [7]. In an exploratory analysis of 183 adults aged 70 or over with memory complaints and a low omega-3 index, 800 mg DHA plus up to 225 mg EPA daily for 3 years produced less decline on one verbal fluency test, which measures word retrieval rather than memory, with no significant differences on the other tests [18].

Does omega-3 lower blood triglycerides?

In trials, yes. In a Cochrane review of 86 randomized trials lasting 12 months or more (162,796 participants), increasing long-chain omega-3 reduced triglycerides by about 15% in a dose-dependent way, rated high-certainty evidence [1]. Trial participants were adults at varying cardiovascular risk, and doses ranged from 0.5 g a day to more than 5 g a day [1]. The review was funded by the UK Medical Research Council [1].

What the evidence does not show

• Attention and processing speed: a meta-analysis found a benefit only in people with cognitive impairment without dementia, a clinical population, and not in healthy subjects [8].
• Mental fatigue: not established. One trial in young adults suggested EPA-rich oil may reduce subjective mental fatigue at times of high demand, and its authors said further investigation is required [10].

In a 5-arm randomized trial in 115 healthy adults, the omega-3 index rose in a dose-dependent manner over about 5 months, with dose alone accounting for 68% of the variability in response, and body weight was another key factor [19].

Algal and fish sources were compared directly in one trial. In a 2-week randomized, open-label trial in 32 healthy adults, 600 mg of DHA a day from algal-oil capsules raised DHA by about 80% in plasma phospholipids and 25% in red blood cells, the same as cooked salmon, and the authors judged the two equivalent [3].

The NIH Office of Dietary Supplements describes commonly reported side effects as usually mild, such as unpleasant taste, heartburn, nausea and diarrhea [35]. The Cochrane review in older adults reported mild gastrointestinal problems as the main side effect, with minor adverse events in fewer than 15% of participants and balanced between groups [5]. A meta-analysis of 90 randomized trials found higher odds of diarrhea (OR 1.257), taste disturbance (OR 3.478) and bleeding tendency (OR 1.260) compared with placebo, and no definite serious adverse events [20]. The Cochrane cardiovascular review found little or no effect on serious adverse events [1].

Pooled data on bleeding are mixed. The 90-trial meta-analysis found higher odds of bleeding tendency [20], while a meta-analysis of 11 randomized trials with 120,643 patients found that bleeding events did not differ between omega-3 and control groups (RR 1.09) [23]. In the subgroup given high-dose purified EPA, the relative risk of bleeding rose 50% while the absolute increase was 0.6% [23]. In 2012, EFSA concluded that supplemental EPA and DHA up to 5 g a day do not increase the risk of reported bleeding episodes in adults [29].

The safety signal reported in two meta-analyses is atrial fibrillation, an irregular heart rhythm [21][22]. In a meta-analysis of 7 cardiovascular outcome trials with 81,210 patients (mean age 65), omega-3 supplements were associated with an increased risk of atrial fibrillation (HR 1.25) [21]. The hazard ratio was 1.49 in trials testing more than 1 g a day and 1.12 in trials testing 1 g a day or less, and the hazard ratio was 1.11 per 1 g higher dose [21].

A 2026 meta-analysis of 35 trials (114,592 people aged 50 and over) found a statistically significant increase only in patients at high cardiovascular risk taking more than 1500 mg a day (OR 1.43; absolute risk difference 0.8%), and lower doses did not appear to raise risk [22]. This differs from the 2021 analysis, which found a smaller but statistically significant increase in trials testing 1 g a day or less [21]. In the 2026 analysis, one author is chief medical officer of a company that sells omega-3 products, one holds stock in an omega-3 blood-testing laboratory, and one received an industry trade-group research award [22]. Evidence is mixed in one respect: the Cochrane review, which pooled a broader arrhythmia outcome, found little or no effect (RR 0.99, low-certainty evidence) [1]. In the two atrial fibrillation analyses, the signal was stronger in higher-dose trials [21][22].

One trial in older adults also reported increased oxidative stress with 18 months of DHA-rich fish oil [9].

Pregnancy and breastfeeding: as of November 12, 2026, the NIH Office of Dietary Supplements fact sheet we checked (as archived) does not report a specific safety finding for omega-3 supplements in pregnancy or breastfeeding [35].

The interaction studies found for this page concern medicines that slow blood clotting: anticoagulants, such as warfarin [24][25][26], and antiplatelet medicines [23]. One published case report describes a warfarin user whose INR rose from 2.8 to 4.3 within a month after she doubled her fish oil from 1000 to 2000 mg a day, and fell after she cut back [24]. A single case cannot show cause.

Larger studies did not find a consistent effect. A retrospective analysis of 573 long-term warfarin users (a clinical population) found that fish and krill oils did not significantly alter time in therapeutic range or bleeding [25]. In a phase I study funded by AstraZeneca, the maker of the prescription omega-3 product tested, 4 g a day of omega-3 carboxylic acids did not affect the pharmacokinetics or pharmacodynamics of warfarin in 26 participants [26]. In pooled bleeding data, risk was linked to the dose of EPA but not to background antiplatelet therapy [23].

If you take any of these medicines, talk to your doctor or pharmacist before combining them with omega-3.