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Awaiting clinical review. This entry is sourced but has not yet been signed off by a pharmacist or clinician.

Fish or algal oil (EPA and DHA)

Omega-3

Omega-3 fish or algal oil reliably lowers blood triglycerides, by about 15% across a Cochrane review of trials, but for preventing heart attacks and strokes the pooled evidence shows little or no effect. It is usually well tolerated, with mild side effects such as fishy taste and stomach upset. The main caution is that pooled trials link marine omega-3 to a higher risk of atrial fibrillation, and the risk rose with dose.

Updated
29 September 2026
Golden fish oil capsules in a small dish
At a glance
Last reviewed 29 September 2026
Evidence
Strong
Best for
Lowering triglycerides
Typical form & use
EPA+DHA oil, up to 4 g daily
Onset
4+ weeks
Safety
Higher doses linked to atrial fibrillation. 1 known interaction, most serious with blood thinners.
Check with your medications →

What it's used for

Evidence is rated per use. The same ingredient can be strong for one thing and traditional for another.

UseEvidenceWhat the research shows
Lowering triglyceridesStrongA Cochrane review found that increasing long-chain omega-3 (EPA and DHA) reduced triglycerides by about 15% in a dose-dependent way, rated high-certainty evidence, mainly from supplement trials. The American Heart Association advises that prescription doses of 4 g a day reduce triglycerides by 30% or more in people with very high levels (500 mg/dL or above). Prescription products are not the same as over-the-counter supplements, so those larger drops should not be assumed from a shop capsule.1,4,8
Preventing heart attack and strokeLimitedA Cochrane review of 86 trials (162,796 people) found little or no effect on all-cause mortality (RR 0.97, 95% CI 0.93 to 1.01), cardiovascular events (RR 0.96, 0.92 to 1.01) or stroke (RR 1.02, 0.94 to 1.12), rated high or moderate certainty. It found a small reduction in coronary heart disease events (RR 0.91, 0.85 to 0.97), rated low certainty. The exception is REDUCE-IT: 4 g a day of a purified EPA prescription drug cut major cardiovascular events from 22.0% to 17.2% (HR 0.75) in 8,179 high-risk people already on statins, but it also raised hospitalisation for atrial fibrillation or flutter (3.1% vs 2.1%). A pooled analysis of 7 large trials (81,210 people) found marine omega-3 raised atrial fibrillation risk (HR 1.25, 1.07 to 1.46), with a higher hazard above 1 g a day (HR 1.49) than at or below it (HR 1.12).1,2,3,8
DepressionLimitedNCCIH reports that a 2021 review of 35 studies (1,964 participants) concluded that if there is an effect it may be too small to be meaningful, and rated the evidence low or very low quality. Other reviews suggest EPA may work better than DHA and that omega-3 may be best added to an antidepressant rather than used instead, but publication bias and differences between trials limit those conclusions.8
Joint pain in rheumatoid arthritisLimitedA 2024 meta-analysis of 23 placebo-controlled trials found a small, statistically uncertain effect on pain (SMD -0.16, 95% CI -0.40 to 0.09) and on tender joint count (SMD -0.20, -0.46 to 0.05), with very low to low certainty. Earlier signs of reduced NSAID use may have been biased by inadequate blinding. We found no review of osteoarthritis pain that we could read, so this rating covers rheumatoid arthritis only.6,8
Dry eyeLimitedThe largest trial, DREAM (535 people with moderate-to-severe dry eye, 3,000 mg EPA+DHA daily for 12 months), found no benefit over an olive oil placebo: symptom score change was -13.9 vs -12.5 points (difference -1.9, 95% CI -5.0 to 1.1), with no difference in tear break-up time or Schirmer test. NCCIH notes that several small studies and a 2022 review of 8 studies (1,107 participants) suggested symptom relief, but the authors flagged small samples and possible bias, so results are mixed.5,8

How much

Ranges below are what studies used and what supplements commonly contain. They are not a recommendation for you. Start at the low end.

Studied range
0.5 to over 5 g EPA+DHA daily1
This is the range across the trials in the Cochrane review (at least 12 months long); 19 trials gave 3 g or more a day. The triglyceride effect grew with dose. Effects on heart outcomes did not differ by dose.
Triglyceride treatment
4 g daily (prescription)4
The American Heart Association advisory covers prescription EPA+DHA or EPA-only at 4 g a day for high triglycerides. EPA+DHA raised LDL cholesterol in very high triglycerides; EPA-only did not.
Dry eye trial dose
3 g daily for 12 months5
This was the DREAM dose of fish-derived EPA+DHA. It did not beat placebo.
Atrial fibrillation and dose
Risk rose with each extra gram2
In the pooled analysis, the atrial fibrillation hazard rose by 1.11 per additional 1 g a day of marine omega-3. We did not open a source that gives an official upper intake limit, so none is stated here.
Timing · No source we read gave advice on time of day.With food? · No source we read gave food guidance. NCCIH lists heartburn, nausea and diarrhoea among the usual mild side effects, so if a capsule upsets your stomach that is worth telling a pharmacist.How long to trial · The triglyceride effect is measured by a blood test, so a repeat test is the only way to know it is working. Nothing you can feel tells you it is protecting your heart, and in DREAM 12 months of a high dose did not improve dry eye symptoms over placebo.

How people take it

Fish oil capsule (EPA and DHA)Varies by product; check EPA+DHA on the labelThe form used in most supplement trials. NCCIH says fish oil supplements contain EPA and DHA.
Algal oilVaries by productNCCIH describes algal oils as a vegetarian source of DHA, with some also containing EPA. We did not read trials specific to algal oil.
Fish liver oil (such as cod liver oil)Varies by productContains EPA and DHA plus vitamins A and D in amounts that vary by product, which can be harmful in excessive amounts (NCCIH).
Prescription icosapent ethyl or EPA+DHA4 g daily (2 g twice daily in REDUCE-IT)Purified prescription products used for high triglycerides. NCCIH notes their composition, testing and regulation differ from supplements, so their effects may not carry over.

Safety

Who should avoid
  • Atrial fibrillation or other rhythm problems — ask first; higher doses raised AF risk
  • Taking blood thinners — ask your prescriber; bleeding evidence is reassuring but limited
  • Very high triglycerides (500 mg/dL or more) — prescription doses are studied; see a clinician
  • Cod liver and other fish liver oils — vitamins A and D can be harmful in excess
Known interactions
MonitorBlood thinners — Omega-3 reduces platelet function, so a bleeding concern is plausible, but a 2014 narrative review found no increase in clinically significant bleeding, including alongside antiplatelet or anticoagulant drugs, and REDUCE-IT saw serious bleeding in 2.7% vs 2.1% on 4 g a day (P=0.06).

Questions people ask

Does fish oil prevent heart attacks?

In pooled trials, mostly no. A Cochrane review of 86 trials found little or no effect on all-cause mortality, cardiovascular events or stroke, and a small reduction in coronary heart disease events (low certainty). One trial of a purified prescription EPA at 4 g a day did cut events in high-risk people on statins, but that result has not been matched by the pooled evidence for ordinary supplements.

Can fish oil cause atrial fibrillation?

It appears so at higher doses. A pooled analysis of 7 large trials found marine omega-3 supplements raised the risk of atrial fibrillation (HR 1.25), with a higher hazard in trials above 1 g a day (HR 1.49) than at or below 1 g (HR 1.12). If you have a heart rhythm condition, ask your doctor before taking it.

Is eating fish better than taking fish oil?

For some conditions, yes. NCCIH says the evidence for benefits from seafood is stronger than for omega-3 supplements, and that other nutrients in seafood, or the foods it replaces, may play a part.

Does fish oil help dry eyes?

The best trial says no. In DREAM, 3,000 mg a day for a year did no better than olive oil placebo on symptoms or tear tests. Some smaller studies were more positive, so results are mixed, but nothing suggests a high dose is worth taking for this alone.

Sources

  1. Systematic review Abdelhamid AS, Brown TJ, Brainard JS, et al. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev. 2020.
  2. Meta-analysis Gencer B, Djousse L, Al-Ramady OT, Cook NR, Manson JE, Albert CM. Effect of Long-Term Marine ɷ-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.
  3. Randomised trial Bhatt DL, Steg PG, Miller M, et al. Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia (REDUCE-IT). N Engl J Med. 2019.
  4. Science advisory Skulas-Ray AC, Wilson PWF, Harris WS, et al. Omega-3 Fatty Acids for the Management of Hypertriglyceridemia: A Science Advisory From the American Heart Association. Circulation. 2019.
  5. Randomised trial Dry Eye Assessment and Management Study Research Group; Asbell PA, Maguire MG, Pistilli M, et al. n-3 Fatty Acid Supplementation for the Treatment of Dry Eye Disease (DREAM). N Engl J Med. 2018.
  6. Systematic review Gkiouras K, Grammatikopoulou MG, Myrogiannis I, et al. Efficacy of n-3 fatty acid supplementation on rheumatoid arthritis' disease activity indicators: a systematic review and meta-analysis of randomized placebo-controlled trials. Crit Rev Food Sci Nutr. 2024.
  7. Narrative review Wachira JK, Larson MK, Harris WS. n-3 Fatty acids affect haemostasis but do not increase the risk of bleeding: clinical observations and mechanistic insights. Br J Nutr. 2014.
  8. Regulator/health agency NCCIH. Omega-3 Supplements: What You Need To Know. National Center for Complementary and Integrative Health.

Last reviewed 29 September 2026 · Next review March 2027 · How we rate evidence