EvidenceBModerateGood evidence in people with one real weakness. New studies could change the answer.
Fish oil capsules didn't clearly prevent heart attacks in most people. The one big exception is a high-dose, purified EPA drug, which cut heart events in high-risk people on statins.
Who it's for
Only high-risk people with high triglycerides on statins, using a prescribed EPA drug.
What to expect
Over-the-counter doses show little or no effect on heart attacks.
Watch out for
Higher risk of the irregular heartbeat atrial fibrillation, and some bleeding.
Fish oil trials show little effect on heart attack
Each dot is a result, and the line shows the range it could plausibly fall in; a range crossing 1 means no clear effect.
← BetterWorse →
No difference
Large trial in older adults (total heart attacks)0.72 (0.59 to 0.9)Clear improvement
Pooled trials (nonfatal heart attack)0.97 (0.87 to 1.08)No clear difference
Pooled trials (heart attack)0.89 (0.76 to 1.04)No clear difference
0.751
risk of heart attack vs. placebo, 1 = same
Fish oil trials show little effect on heart attack
Figure 2. Associations of Omega-3 Fatty Acids With Subtypes of Coronary Heart Disease and Major Vascular Events, by Trial Symbols and conventions as in Figure 1.
The FDA allows a label claim that EPA and DHA "may reduce the risk of coronary heart disease," calling the research supportive but not conclusive. It says supplement labels shouldn't recommend more than 2 g a day of EPA and DHA1Guideline · 2026Omega-3 Fatty Acids: Fact Sheet for Health ProfessionalsThis health claim states, “Supportive but not conclusive research shows that consumption of EPA and DHA omega-3 fatty acids may reduce the risk of coronary heart disease.” FDA also specifies that the labels of dietary supplements should not recommend a daily intake of EPA and DHA higher than 2 g.NIH Office of Dietary Supplements.
What the studies show
A Cochrane review pooled 86 trials (162,796 people, 12 to 88 months). Omega-3 made little or no difference to death from any cause, stroke or overall heart events. It may slightly lower heart disease events: about 1 fewer person in 167 treated, and 1 in 334 for heart disease deaths. Certainty for those was low5Meta-analysis · 2020 · 162,796 peopleOmega-3 fatty acids for the primary and secondary prevention of cardiovascular disease.This is the most extensive systematic assessment of effects of omega-3 fats on cardiovascular health to date. Moderate- and low-certainty evidence suggests that increasing LCn3 slightly reduces risk of coronary heart disease mortality and events, and reduces serum triglycerides (evidence mainly from supplement…Cochrane Database Syst Rev.
A review of 10 large trials (77,917 high-risk people, average 4.4 years) found no clear link to fewer heart attacks, heart disease deaths or major vascular events. This included people with prior heart disease, diabetes or statin use3Meta-analysis · 2018 · 500 peopleAssociations of Omega-3 Fatty Acid Supplement Use With Cardiovascular Disease Risks: Meta-analysis of 10 Trials Involving 77 917 Individuals.This meta-analysis demonstrated that omega-3 fatty acids had no significant association with fatal or nonfatal coronary heart disease or any major vascular events. It provides no support for current recommendations for the use of such supplements in people with a history of coronary heart disease.JAMA Cardiol.
A review of 38 trials (149,051 people) found a small drop in non-fatal heart attacks (13% lower relative risk How much more or less likely something is in one group than another, as a ratio. A big relative change can still be a small change for any one person.). The drop was larger with EPA alone (28% lower) than with EPA plus DHA (8% lower)2Meta-analysis · 2021 · 149,051 peopleEffect of omega-3 fatty acids on cardiovascular outcomes: A systematic review and meta-analysis.Omega-3 FAs reduced cardiovascular mortality and improved cardiovascular outcomes. The cardiovascular risk reduction was more prominent with EPA monotherapy than with EPA+DHA.EClinicalMedicine. Such figures compare groups, so one person's gain depends on their starting risk.
In a trial of 8,179 statin-treated people with high triglycerides, 4 g a day of purified EPA (icosapent ethyl) cut major heart events: 17.2% vs 22.0% on a dummy pill (placebo A dummy treatment that looks like the real one, so people can't tell which they got.), for 4.9 years. It was industry funded4Randomized trial · 2019 · 8,179 peopleCardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia.Among patients with elevated triglyceride levels despite the use of statins, the risk of ischemic events, including cardiovascular death, was significantly lower among those who received 2 g of icosapent ethyl twice daily than among those who received placebo. (Funded by Amarin Pharma; REDUCE-IT ClinicalTrials.gov…N Engl J Med.
Other large trials found no benefit. A 13,078-person trial of EPA plus DHA at 4 g a day was stopped early, with events at 12.0% vs 12.2% on corn oil6Randomized trial · 2020 · 6,539 peopleEffect of High-Dose Omega-3 Fatty Acids vs Corn Oil on Major Adverse Cardiovascular Events in Patients at High Cardiovascular Risk: The STRENGTH Randomized Clinical Trial.Among statin-treated patients at high cardiovascular risk, the addition of omega-3 CA, compared with corn oil, to usual background therapies resulted in no significant difference in a composite outcome of major adverse cardiovascular events. These findings do not support use of this omega-3 fatty acid formulation to…JAMA. A trial of 15,480 people with diabetes (1 g a day, 7.4 years)9Randomized trial · 2018 · 15,480 peopleEffects of n-3 Fatty Acid Supplements in Diabetes Mellitus.Among patients with diabetes without evidence of cardiovascular disease, there was no significant difference in the risk of serious vascular events between those who were assigned to receive n-3 fatty acid supplementation and those who were assigned to receive placebo. (Funded by the British Heart Foundation and…N Engl J Med and one of 1,027 older adults after a heart attack (1.8 g a day, 2 years)8Randomized trial · 2021 · 1,027 peopleEffects of n-3 Fatty Acid Supplements in Elderly Patients After Myocardial Infarction: A Randomized, Controlled Trial.We could not detect reduction in clinical events in our elderly patients with recent AMI who were treated with 1.8 g n-3 PUFAs daily for 2 years. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT01841944.Circulation also found none.
In 25,871 people at usual risk (1 g a day, 5.3 years), major heart events did not differ clearly. Heart attacks were 28% lower in a secondary result that could be chance10Randomized trial · 2019 · 25,871 peopleMarine n-3 Fatty Acids and Prevention of Cardiovascular Disease and Cancer.Supplementation with n-3 fatty acids did not result in a lower incidence of major cardiovascular events or cancer than placebo. (Funded by the National Institutes of Health and others; VITAL ClinicalTrials.gov number, NCT01169259 .).N Engl J Med.
Key studies
Study
Who
What it found
Trial, 20194Randomized trial · 2019 · 8,179 peopleCardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia.Among patients with elevated triglyceride levels despite the use of statins, the risk of ischemic events, including cardiovascular death, was significantly lower among those who received 2 g of icosapent ethyl twice daily than among those who received placebo. (Funded by Amarin Pharma; REDUCE-IT ClinicalTrials.gov…N Engl J Med
8,179 high-risk people on statins
Purified EPA 4 g cut major heart events (17.2% vs 22.0%)
Trial, 20206Randomized trial · 2020 · 6,539 peopleEffect of High-Dose Omega-3 Fatty Acids vs Corn Oil on Major Adverse Cardiovascular Events in Patients at High Cardiovascular Risk: The STRENGTH Randomized Clinical Trial.Among statin-treated patients at high cardiovascular risk, the addition of omega-3 CA, compared with corn oil, to usual background therapies resulted in no significant difference in a composite outcome of major adverse cardiovascular events. These findings do not support use of this omega-3 fatty acid formulation to…JAMA
13,078 high-risk people on statins
EPA+DHA 4 g: no difference (12.0% vs 12.2%)
Trial, 201910Randomized trial · 2019 · 25,871 peopleMarine n-3 Fatty Acids and Prevention of Cardiovascular Disease and Cancer.Supplementation with n-3 fatty acids did not result in a lower incidence of major cardiovascular events or cancer than placebo. (Funded by the National Institutes of Health and others; VITAL ClinicalTrials.gov number, NCT01169259 .).N Engl J Med
25,871 people at usual risk
No clear drop in major heart events
Review of 86 trials, 20205Meta-analysis · 2020 · 162,796 peopleOmega-3 fatty acids for the primary and secondary prevention of cardiovascular disease.This is the most extensive systematic assessment of effects of omega-3 fats on cardiovascular health to date. Moderate- and low-certainty evidence suggests that increasing LCn3 slightly reduces risk of coronary heart disease mortality and events, and reduces serum triglycerides (evidence mainly from supplement…Cochrane Database Syst Rev
162,796 adults
Little or no effect on most outcomes; slight drop in heart disease events
Review of 38 trials, 20212Meta-analysis · 2021 · 149,051 peopleEffect of omega-3 fatty acids on cardiovascular outcomes: A systematic review and meta-analysis.Omega-3 FAs reduced cardiovascular mortality and improved cardiovascular outcomes. The cardiovascular risk reduction was more prominent with EPA monotherapy than with EPA+DHA.EClinicalMedicine
149,051 people
Heart attacks down; EPA alone helped more
Safety
Common side effects are usually mild: unpleasant taste, bad breath, heartburn, nausea, diarrhea, headache1Guideline · 2026Omega-3 Fatty Acids: Fact Sheet for Health ProfessionalsThis health claim states, “Supportive but not conclusive research shows that consumption of EPA and DHA omega-3 fatty acids may reduce the risk of coronary heart disease.” FDA also specifies that the labels of dietary supplements should not recommend a daily intake of EPA and DHA higher than 2 g.NIH Office of Dietary Supplements. Omega-3 raised atrial fibrillation risk by 26% relative to controls, and EPA alone raised bleeding risk by 49%2Meta-analysis · 2021 · 149,051 peopleEffect of omega-3 fatty acids on cardiovascular outcomes: A systematic review and meta-analysis.Omega-3 FAs reduced cardiovascular mortality and improved cardiovascular outcomes. The cardiovascular risk reduction was more prominent with EPA monotherapy than with EPA+DHA.EClinicalMedicine. In the EPA trial, hospitalization for atrial fibrillation was 3.1% vs 2.1%, and serious bleeding 2.7% vs 2.1%4Randomized trial · 2019 · 8,179 peopleCardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia.Among patients with elevated triglyceride levels despite the use of statins, the risk of ischemic events, including cardiovascular death, was significantly lower among those who received 2 g of icosapent ethyl twice daily than among those who received placebo. (Funded by Amarin Pharma; REDUCE-IT ClinicalTrials.gov…N Engl J Med. Stomach side effects hit 24.7% vs 14.7% on corn oil in the high-dose EPA+DHA trial6Randomized trial · 2020 · 6,539 peopleEffect of High-Dose Omega-3 Fatty Acids vs Corn Oil on Major Adverse Cardiovascular Events in Patients at High Cardiovascular Risk: The STRENGTH Randomized Clinical Trial.Among statin-treated patients at high cardiovascular risk, the addition of omega-3 CA, compared with corn oil, to usual background therapies resulted in no significant difference in a composite outcome of major adverse cardiovascular events. These findings do not support use of this omega-3 fatty acid formulation to…JAMA. Prescription EPA is a drug, so a clinician decides if it is appropriate.
What we don't know
Why purified EPA worked in one trial while EPA+DHA did not. Corn oil as the comparison in some trials may have affected results.
Whether ordinary supplements at usual doses help any group.
Written by AI from the studies listed, without review by a clinician, and graded with the GRADE method. It can be wrong, so check the studies it cites. Education, not medical advice.