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Omega-3 fatty acids (fish oil)

Fats found in oily fish and sold as fish oil, studied for heart disease, triglycerides, depression, memory and thinking, and rheumatoid arthritis.

Explained simply · Last reviewed

What it is

Omega-3s are fats found in foods such as fish and flaxseed, and in supplements such as fish oil. ODS, the NIH Office of Dietary Supplements, says the two found in fish are EPA and DHA. It says interest in their effects on the heart was spurred by research dating back to the 1970s. That research found low rates of heart attacks and other coronary events among Greenland Inuit and other fish-eating populations, such as those in Japan.

More about Omega-3 fatty acids (fish oil)

ODS, the NIH Office of Dietary Supplements, says the two found in fish are EPA and DHA. It says interest in their effects on the heart was spurred by research dating back to the 1970s. That research found low rates of heart attacks and other coronary events among Greenland Inuit and other fish-eating populations, such as those in Japan.

ODS says microalgae at the base of the marine food chain make EPA and DHA, not the fish. Fish take them in as the microalgae move up the food chain, and store them in their tissues. ODS reports that fish oil is one of the most commonly used supplements, other than vitamins and minerals, among US adults and children. ODS and NCCIH, the US agency that studies complementary medicine, each review the research on omega-3s for heart disease, triglycerides, depression, Alzheimer’s disease and cognitive function, and rheumatoid arthritis.

A third omega-3, ALA, comes from plants. NCCIH lists flaxseed, soybean and canola oils, chia seeds and walnuts. ODS says the body can convert ALA into EPA and DHA, but only in very limited amounts. It says DHA is especially high in the retina and the brain, and that omega-3s are part of the membranes of cells.

NCCIH lists supplements of fish oil, fish liver oil such as cod liver oil, krill oil and algal oil, which it describes as a vegetarian source. There are also prescription omega-3 medicines. NCCIH describes them as a separate kind of product: they differ in composition, and are tested and regulated differently from supplements. Where a source says which kind it studied, the claims below say so.

Also known as: fish oil, EPA, DHA, eicosapentaenoic acid, docosahexaenoic acid, n-3 fatty acids, krill oil, algal oil, cod liver oil

At a glance

Safety: known risks, 4 groups who should avoid it or take extra care and 1 documented interaction. See Safety ↓

Claims made about Omega-3 fatty acids (fish oil), and how strong the evidence is for each:

Longevity and aging claims

Claims made about Omega-3 fatty acids (fish oil) and aging, and how strong the evidence is for each. A change in a marker is not the same as a longer life.

Each rating follows our published rules and the sources cited for it. We don’t add our own medical judgment. How we rate

Safety

Read this before the ratings below.

Risks

  • NCCIH and ODS describe side effects as usually mild. They list an unpleasant taste, bad breath, bad-smelling sweat, headache, heartburn, nausea, stomach discomfort, and diarrhea.
  • Atrial fibrillation (an irregular heart rhythm): ODS reports that two large clinical trials found that "taking 4 g/day of omega-3 supplements for several years slightly increased the risk of atrial fibrillation in people with CVD or at high risk of CVD". ODS describes the products tested in those two trials as high-dose prescription forms of omega-3s.
  • In 2023 the European Medicines Agency’s safety committee (PRAC) added atrial fibrillation as a common side effect of prescription medicines containing omega-3-acid ethyl esters, which are used to treat high triglycerides. It based this on systematic reviews and meta-analyses of trials showing a dose-dependent increase in risk, compared with placebo, in patients with established cardiovascular disease or cardiovascular risk factors, and states that the risk observed is highest with a dose of "4 g/daily". It states that if atrial fibrillation develops, treatment should be permanently discontinued. This statement concerns those medicines.
  • Bleeding and immune function: ODS reports that the US Institute of Medicine set no upper intake level for omega-3s, but noted that high doses of DHA and/or EPA might reduce immune function by suppressing inflammatory responses, and that, in its words, "Doses of 2–15 g/day EPA and/or DHA might also increase bleeding time by reducing platelet aggregation".
  • ODS also reports that the European Food Safety Authority found long-term EPA and DHA supplement intakes of "up to about 5 g/day" appear to be safe, and had not been shown to cause bleeding problems or affect immune function, and that the FDA has concluded that supplements providing "no more than 5 g/day EPA and DHA are safe when used as recommended". ODS notes that the two atrial fibrillation trials above were completed after these assessments.

Who should avoid it or take extra care

  • People taking warfarin (Coumadin) or similar anticoagulants: ODS lists this as a possible interaction, described below.
  • People with cardiovascular disease, or at high risk of it: ODS reports the increase in atrial fibrillation from two trials of high-dose prescription omega-3 products in these groups, and the European Medicines Agency reports a dose-dependent increase in risk in patients with established cardiovascular disease or cardiovascular risk factors treated with prescription omega-3-acid ethyl ester medicines.
  • People taking cod liver oil: NCCIH notes it also contains vitamins A and D, in amounts that vary from product to product, and that these vitamins can be harmful in excessive amounts.
  • People with depression or rheumatoid arthritis: NCCIH advises anyone who may have depression to consult a health care provider, and advises people with rheumatoid arthritis not to change their prescribed medications without consulting theirs.

Documented interactions

  • Warfarin (Coumadin) and similar anticoagulants: ODS states that fish oil can have antiplatelet effects at high doses, and might prolong clotting times, shown by a raised INR, when taken with warfarin. It adds that most research indicates that doses of "3–6 g/day fish oil" do not significantly affect the anticoagulant status of people taking warfarin, and that a 2014 review concluded omega-3s do not affect the risk of clinically significant bleeding. It reports that the FDA-approved package inserts for prescription omega-3 medicines state that people taking them with anticoagulants should be monitored periodically for changes in INR. Source [1]

Safety sources: Source [1]Source [2]Source [3]

What the evidence says

Each claim is rated on its own evidence. Ratings follow the scale on our methodology page.

  • Lowers blood triglycerides Evidence rating: Strong

    People with high triglycerides take it hoping it will bring them down.

    A 2020 Cochrane review found that increasing EPA and DHA lowers fasting triglycerides by about 15%, and rated this high certainty.

    NCCIH describes triglycerides as a type of fat in the body. It says excessive levels may raise the risk of heart disease. A 2020 Cochrane review looked at randomized trials lasting at least a year. It found that increasing EPA and DHA lowers fasting triglycerides by about 15%, in 27 trials with 43,998 participants. It rated this outcome high certainty. The reduction was larger at higher intakes. The review found little or no effect on total, HDL or LDL cholesterol, or on body mass index, also at high certainty. Its evidence came mainly from supplement trials.

    ODS reports the figure of about 15% from this review. NCCIH reports the same figure, citing a 2020 review of 23 studies with 43,998 participants. Both state that EPA and DHA supplements lower triglycerides. ODS also reports an analysis of 58 trials. It found a dose-response relationship between lower-dose omega-3 intakes, from diet and supplements, and triglyceride levels. The effect was stronger in people whose triglycerides were higher to begin with.

    NCCIH notes that several prescription omega-3 medicines are approved to lower very high triglycerides. It states that their composition differs from typical supplements, and that their effects may not be the same. This rating is about the triglyceride level itself. Heart attacks, strokes and deaths are rated separately in the next two claims. The review’s bleeding and blood-clot findings are in the next claim.

    Sources: Source [1]Source [2]Source [3]

  • Lowers overall rates of cardiovascular events, stroke, and death Evidence rating: Evidence against

    People take it hoping to lower their risk of heart attack, stroke and death from heart disease.

    A 2020 Cochrane review found little or no effect on cardiovascular events or death from any cause (high certainty), and probably little or no difference to cardiovascular death or stroke (moderate).

    A 2020 Cochrane review pooled 86 randomized trials in 162,796 adults. Most tested EPA and DHA capsules for at least a year. It found that increasing EPA and DHA has little or no effect on death from any cause or on cardiovascular events (high-certainty evidence). It found that increasing EPA and DHA probably makes little or no difference to cardiovascular death or stroke (moderate-certainty evidence). Effects did not differ by dose or trial length. On harms, the review found the effect on bleeding, and on pulmonary embolism or deep vein thrombosis, unclear. It rated that evidence very low certainty.

    ODS reports similar conclusions from several earlier reviews and a 2016 report by the US Agency for Healthcare Research and Quality. They concluded that omega-3 supplements do not appear to significantly reduce the risk of most cardiovascular events. ODS notes that many of them did find a reduced risk of cardiac death. The sources do not all agree. ODS describes the same Cochrane review as finding a slight decrease in cardiovascular death. ODS and NCCIH both describe a 2019 meta-analysis of 13 trials that found lower rates of heart attack and coronary heart disease. ODS reports that it also found lower rates of cardiovascular death and total cardiovascular disease. Following this site’s rule, the lower rating is shown.

    ODS also describes two trials of high-dose prescription omega-3 medicines. REDUCE-IT tested an EPA-only drug in statin users with cardiovascular disease, or with diabetes and other risk factors, and found fewer cardiovascular events. STRENGTH tested an EPA-plus-DHA drug in people at high cardiovascular risk and found no significant benefit. ODS states that the reasons for the different results are not clear. It points to differences in the omega-3 formulation: EPA as an ethyl ester in REDUCE-IT, and EPA and DHA as carboxylic acids in STRENGTH. It also points to differences in the baseline health of the people studied.

    Beyond those, ODS suggests that part of the explanation may lie with the different placebos: mineral oil in REDUCE-IT and corn oil in STRENGTH. It states that mineral oil is not a neutral placebo. It says the difference between the groups in REDUCE-IT would likely have been smaller with a more neutral placebo oil. More generally, ODS states that several factors might explain some of the conflicting findings among trials. It names the omega-3 form, the study population, background dietary omega-3 intake, and the use of statins and other heart medicines. It adds that dose probably plays a major role.

    Sources: Source [1]Source [2]Source [3]

  • Lowers the risk of coronary heart disease events and coronary deaths Evidence rating: Limited

    People take it hoping to lower their risk of heart attacks and of dying from coronary heart disease.

    A 2020 Cochrane review found that increasing EPA and DHA may slightly reduce coronary heart disease deaths and events, and rated this low certainty.

    The 2020 Cochrane review of 86 trials also found that increasing EPA and DHA may slightly reduce coronary heart disease deaths and coronary events, such as heart attacks. It rated this evidence low certainty. It estimated that 334 people would need to increase their EPA and DHA to prevent one coronary death, and 167 to prevent one coronary event.

    ODS concludes that omega-3 supplements might reduce the risk of some cardiovascular endpoints, especially in people with low dietary omega-3 intakes. It says evidence of protection is stronger for people with existing coronary heart disease than for healthy people. NCCIH states there is some evidence that people with heart disease or high triglycerides may benefit from omega-3 supplements.

    ODS reports that the FDA allows a qualified health claim for EPA and DHA. The claim says that "supportive but not conclusive research" shows they may reduce the risk of coronary heart disease.

    Sources: Source [1]Source [2]Source [3]

  • Improves symptoms of depression Evidence rating: Limited

    People with depression take it hoping it will ease their symptoms.

    A 2021 Cochrane review found a small-to-modest improvement in depressive symptoms, unlikely to be clinically meaningful, and rated the evidence very low certainty.

    A 2021 Cochrane review looked at 35 trials in adults with major depressive disorder. It found a small-to-modest improvement in depressive symptoms with omega-3 supplements compared with placebo. The reviewers judged this unlikely to be clinically meaningful and rated the evidence very low certainty. They also found signs that this estimate may be biased toward a positive result.

    They found no evidence of a difference in remission or response rates (low-certainty evidence). They concluded that there is not enough high-certainty evidence to determine the effects of omega-3s as a treatment for major depression. Only one small trial compared omega-3s with an antidepressant. Its results were too imprecise to rule out important benefit or harm either way.

    NCCIH states it is uncertain whether omega-3 supplements help depression. It adds that other reviews have suggested that, if there is an effect, EPA may be more beneficial than DHA. Those reviews also suggested omega-3s may be best used alongside antidepressants rather than in place of them. NCCIH says publication bias and differences between trials mean more high-quality studies are needed.

    Sources: Source [1]Source [2]

  • Slows decline in Alzheimer’s disease Evidence rating: Evidence against

    People with Alzheimer’s disease, or those caring for them, try it hoping it will slow the decline.

    A 2016 Cochrane review found no evidence of benefit at six months on cognitive function, daily living or dementia severity in mild to moderate Alzheimer’s disease, rating these high quality.

    A 2016 Cochrane review, searching to December 2015, found three placebo-controlled trials of omega-3 supplements in 632 people with mild to moderate Alzheimer’s disease. The trials lasted 6 to 18 months. At six months the review found no evidence of benefit on cognitive function, activities of daily living, dementia severity, quality of life, or mental health. It rated the evidence for these outcomes high quality. One very small study, of 22 people, showed a benefit on everyday practical tasks after 12 months (moderate-quality evidence). The reviewers found no trials in other types of dementia, and state that effects in other populations remain unclear.

    ODS states that, overall, reviews indicate omega-3 supplementation does not affect cognitive function in people with Alzheimer’s disease. NCCIH describes a review that found no effect on cognition in people already diagnosed.

    A 2024 meta-analysis disagrees in part. It found slower progression on one dementia-severity scale. That result came from two studies with 485 participants, one of which tested Souvenaid, a multi-nutrient product. It found no statistically significant difference on the other cognitive and daily-living scales it examined. Its authors describe the evidence of cognitive improvement as inconclusive. Following this site’s rule, the lower rating is shown.

    Sources: Source [1]Source [2]Source [3]Source [4]

  • Protects memory and thinking in healthy older adults Evidence rating: Evidence against

    Healthy older adults take it hoping to keep their memory and thinking sharp.

    A 2012 Cochrane review of three trials in cognitively healthy people aged 60 and over found no benefit on cognition; ODS reports the same, while NCCIH describes a review suggesting protection.

    A 2012 Cochrane review found three high-quality trials in cognitively healthy people aged 60 and over, with cognitive data on 3,536 participants. It found no benefit of omega-3 supplementation on cognitive function over periods of up to 40 months. None of the trials measured whether people developed dementia, so the reviewers state that direct evidence on dementia is lacking. People in both groups showed little or no cognitive decline during the trials. The reviewers called for longer studies, which might be better able to detect an effect.

    ODS states in its 2025 fact sheet that reviews overall indicate omega-3 supplementation does not affect cognitive function in healthy older adults. NCCIH describes a 2022 review of 33 studies. That review suggests omega-3s from diet and supplements may have a protective effect against cognitive decline in healthy people. Following this site’s rule, the lower rating is shown.

    ODS adds that omega-3s may improve some aspects of cognitive function in people with mild cognitive impairment, but that this needs to be confirmed in further trials. That group is not rated here.

    Sources: Source [1]Source [2]Source [3]

  • Eases rheumatoid arthritis symptoms Evidence rating: Limited

    People with rheumatoid arthritis take it hoping to ease joint pain, swelling and stiffness.

    ODS states that omega-3s may be helpful alongside drug treatment for rheumatoid arthritis symptoms, but that review findings are inconsistent and more research is needed.

    ODS reports on clinical trials in people with rheumatoid arthritis, many of them from the 1990s. It says the trials have generally found that omega-3 supplements reduce the use of anti-inflammatory drugs and corticosteroids. They have not had consistent effects on painful or tender joints, joint swelling, or morning stiffness.

    ODS describes reviews and meta-analyses as inconsistent. Some find no significant effect on symptoms but reduced drug use. Others find less joint swelling, pain and morning stiffness. ODS concludes that omega-3s may be helpful alongside drug treatment for rheumatoid arthritis symptoms, but that more research is needed to confirm this.

    NCCIH describes a 2021 review in which diets rich in omega-3s led to less pain than ordinary diets. The review’s authors noted that the evidence was low. NCCIH also describes a 2022 review suggesting that eating foods rich in polyunsaturated fats, especially omega-3s, may improve symptoms. As NCCIH describes them, both of those reviews concern diets rather than supplements.

    Sources: Source [1]Source [2]

Longevity and aging

What the cited sources report about lifespan, death from any cause, and markers studied in connection with aging. A change in a marker is not the same as a longer life. Each outcome is rated on its own evidence, on the same scale as the claims above.

  • Lowers the risk of death from any cause in adults Evidence rating: Evidence against

    People take it hoping it will help them live longer.

    A 2020 Cochrane review of 45 trials found that increasing EPA and DHA has little or no effect on death from any cause, and rated this high certainty.

    A 2020 Cochrane review looked at randomized trials in adults lasting at least a year, most of them testing EPA and DHA capsules. It found that increasing EPA and DHA has little or no effect on death from any cause. The risk ratio was 0.97 (95% confidence interval 0.93 to 1.01), from 45 trials with 143,693 participants and 11,297 deaths. The review rated this high-certainty evidence. It found that effects did not differ by trial length or dose.

    ODS reports the same review, among its recent reviews and meta-analyses, as finding that the supplements did not affect all-cause mortality. In its account of initial clinical research, ODS also describes an earlier systematic review of seven trials published between 1966 and 2005. Six of them were secondary-prevention trials. That review’s authors concluded that omega-3s from fish and fish oil supplements reduce all-cause mortality. Cardiovascular and coronary deaths are rated separately in the claims above.

    Sources: Source [1]Source [2]

  • Slows DNA-methylation (epigenetic) clocks Evidence rating: Limited

    People take it hoping it will slow the aging of their body.

    In a post hoc analysis of a trial in Swiss adults 70 and over, the authors report omega-3 slightly slowed three of four aging clocks, and call the changes’ meaning for long-term survival unknown.

    DNA-methylation clocks are calculated from blood samples, and the DO-HEALTH authors describe them as clocks of biological aging. This entry is about those clocks: no study cited here measured lifespan or death. In DO-HEALTH, 777 Swiss adults aged 70 and over took an algae-derived omega-3 supplement or a placebo for three years. The authors report that omega-3 slowed three of the four clocks they focused on (PhenoAge, GrimAge2 and DunedinPACE), but not the fourth, GrimAge. They describe the effect as small.

    They describe the work as a post hoc analysis. They note that the Swiss participants were healthier, and started with lower blood omega-3 levels, than the trial as a whole. They state that the significance of the clock changes for long-term survival is unknown. It is a single trial, so this page rates the evidence limited.

    A second trial measured a different marker. A sub-study of 1,031 participants in the US VITAL trial measured telomere length in white blood cells. A marine omega-3 supplement showed no significant difference from placebo in its change, at two or four years.

    DO-HEALTH was funded in part by companies including Roche, Pfizer and NESTEC. One of its authors works for Altos Labs, a biotechnology company. That author founded a nonprofit foundation that has licensed patents for epigenetic clocks, including GrimAge.

    Sources: Source [1]Source [2]

How and when to take it

What the cited sources say about taking it. Ask your doctor or pharmacist what applies to you.

  • Check the label for how much EPA and DHA it contains

    ODS states that omega-3 supplement formulations vary widely, and that the label is where to find which omega-3s a product contains and how much of each. Source [1]

  • A prescription omega-3 is not the same product as a supplement

    NCCIH states that the prescription omega-3 medicines approved to lower very high triglycerides differ in composition from typical omega-3 supplements, and are tested and regulated differently, so their effects may not be the same as those of supplements. Source [1]

  • Tell your doctor or pharmacist if you take warfarin or another anticoagulant

    ODS lists warfarin and similar anticoagulants as a possible interaction, described below, and advises people taking medications regularly to discuss possible interactions with their health care providers. Source [1]

Which form the evidence used

Supplements are sold in several forms. This is what the sources on this page say about them — which form the research used, and any comparison those sources themselves made. Where they made none, this page does not rank the forms.

  • Fish oil capsules providing EPA and DHA, What the sources supportDetails

    The 2020 Cochrane review on cardiovascular disease reports that most of its EPA and DHA trials gave capsules and few gave oily fish; NCCIH describes 65 of its 86 trials as using supplement capsules. The review abstracts cited here do not report results by chemical form. Separately, ODS reports that omega-3s as natural triglycerides, re-esterified triglycerides, and free fatty acids have somewhat higher bioavailability than ethyl esters, but that all of these forms significantly raise EPA and DHA levels in the blood. That is a statement about absorption, not about whether any form works better for the claims rated below. Source [1]Source [2]Source [3]

  • Krill oil, Details

    ODS reports that krill oil carries omega-3s mainly as phospholipids, and that some studies suggest these have somewhat higher bioavailability than the omega-3s in fish oil while other studies do not. None of the sources cited here rated krill oil for any of the claims below. Source [1]

  • Algal oil (vegetarian), Details

    NCCIH describes algal oils as a vegetarian source of DHA, some of which also contain EPA. ODS notes that the fish themselves get EPA and DHA from microalgae, and reports that a small study found DHA from algal oil was as bioavailable as DHA from cooked salmon. None of the sources cited here rated algal oil for any of the claims below. Source [1]Source [2]

  • Cod liver oil, Details

    NCCIH states that fish liver oils such as cod liver oil contain EPA and DHA and also vitamins A and D, in amounts that vary from product to product, and that vitamins A and D can be harmful in excessive amounts. Source [1]

  • Flaxseed oil and other plant sources of ALA, What the sources supportDetails

    ALA is a different omega-3. The 2020 Cochrane review analyzed it separately from EPA and DHA and reached separate conclusions for it; the ratings on this page are for EPA and DHA only. ODS reports that the body converts only a small share of ALA into EPA and DHA, with reported rates of less than 15%. Source [1]Source [2]

Also documented elsewhere on this site

Other supplements we cover that document an interaction with the same thing. This is a pointer to what those pages say, not a statement about taking them together — we have no source reviewing these in combination.

Sources

  1. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease
    Cochrane Database of Systematic Reviews, 2020 · Systematic review · Primary source · Certainty: very low
  2. Omega-3 Fatty Acids: Fact Sheet for Health Professionals
    NIH Office of Dietary Supplements, 2025 · Health authority summary · Primary source
  3. Omega-3 Supplements: What You Need To Know
    National Center for Complementary and Integrative Health, NIH, 2024 · Health authority summary · Primary source
  4. Omega-3 fatty acids for depression in adults
    Cochrane Database of Systematic Reviews, 2021 · Systematic review · Primary source · Certainty: very low
  5. Omega-3 fatty acids for the treatment of dementia
    Cochrane Database of Systematic Reviews, 2016 · Systematic review · Primary source · Certainty: moderate
  6. The effects of omega-3, DHA, EPA, Souvenaid® in Alzheimer's disease: A systematic review and meta-analysis
    Neuropsychopharmacology Reports, 2024 · Meta-analysis · Primary source
  7. Omega 3 fatty acid for the prevention of cognitive decline and dementia
    Cochrane Database of Systematic Reviews, 2012 · Systematic review · Primary source
  8. Individual and additive effects of vitamin D, omega-3 and exercise on DNA methylation clocks of biological aging in older adults from the DO-HEALTH trial
    Nature Aging, 2025 · Randomized controlled trial · Supporting source
    This source discloses industry funding.
    Some of its authors disclose ties to industry.
  9. Vitamin D3 and marine ω-3 fatty acids supplementation and leukocyte telomere length: 4-year findings from the VITamin D and OmegA-3 TriaL (VITAL) randomized controlled trial
    The American Journal of Clinical Nutrition, 2025 · Randomized controlled trial · Supporting source
    This source discloses industry funding.
  10. Meeting highlights from the Pharmacovigilance Risk Assessment Committee (PRAC) 25-28 September 2023
    European Medicines Agency, 2023 · Health authority summary · Primary source

Page history

Show all 3 changes to this page
  • — Rewritten to the content style guideline; ratings and sources unchanged.
  • — Added a longevity section. Death from any cause in adults rated evidence-against on the 2020 Cochrane review's high-certainty finding; slowing of DNA-methylation (epigenetic) clocks rated limited on a single trial.
  • — Published. All seven claims, the safety section and every source passed the site's source and wording reviews. The uncited atrial-fibrillation meta-analysis stays logged in docs/08-open-decisions.md.