Does fish oil prevent heart attacks?

What large reviews found

The 2020 Cochrane review pooled 86 trials with 162,796 adults, who took omega-3 for 12 to 88 months.^[1] It reported these results for EPA and DHA:^[1]

• coronary events 9% lower, so about 167 people need more omega-3 to prevent one event (low certainty)^[1]
• coronary deaths 10% lower, so about 334 people for one death prevented (low certainty)^[1]
• little or no effect on all cardiovascular events, stroke, arrhythmia or death from any cause^[1]

A 2019 review of 13 trials and 127,477 people reached a more positive result.^[3] Even without the REDUCE-IT trial, it found 8% fewer heart attacks, 8% fewer coronary deaths and 7% fewer cardiovascular deaths.^[3] The benefit for all cardiovascular events was 3%, and it grew with the dose.^[3] The Cochrane review found no such link with the dose.^[1] The effects in both reviews are small.^[1][3]

What the large trials found

The trials differ in people, dose and product:

• VITAL: 25,871 US adults with no previous heart attack or stroke took 1 g of fish oil a day for 5.3 years. Major cardiovascular events did not fall significantly (386 against 419), but heart attacks were 28% lower.^[2][4]
• ASCEND: 15,480 people with diabetes and no heart disease took 1 g a day for 7.4 years. Serious vascular events were 8.9% against 9.2%, with no significant difference.^[5]
• GISSI-Prevenzione: 11,324 people who had a recent heart attack took 1 g a day for 3.5 years. Death, heart attack and stroke combined fell by 10%.^[6] The trial was open-label, so people knew what they took.^[4]
• REDUCE-IT: 8,179 people on statins, with high triglycerides and heart disease or diabetes, took 4 g a day of purified EPA, a prescription medicine, for 4.9 years. Events were 17.2% against 22.0%. Amarin Pharma paid for the trial.^[7]
• STRENGTH: 13,078 people at high risk took 4 g a day of a prescription EPA and DHA product. Events were 12.0% against 12.2%, and the trial stopped early.^[8]
• PISCES: 1,228 people on hemodialysis took fish oil with 1.6 g of EPA and 0.8 g of DHA a day for 3.5 years. Serious cardiovascular events were 43% lower.^[9]

Why the trials disagree

The form of omega-3, the people studied, their usual fish intake, their other medicines and the dose may all explain part of the differences.^[4] The placebo may matter too. REDUCE-IT used mineral oil, which is not neutral: it affects blood fats and markers of inflammation, so the true difference is probably smaller.^[4] STRENGTH used corn oil.^[8]

A 2026 review looked at high-dose trials. Among blinded trials against a placebo, only 4 g a day of icosapent ethyl, a purified EPA, was linked to fewer cardiovascular events.^[10] Its search ended in May 2025, before PISCES was published.^[10] That prescription product differs from a fish oil capsule, so its effects may not apply to supplements.^[11]

Who should be careful

High doses raised atrial fibrillation in people at high heart risk: see Can fish oil cause atrial fibrillation?.^[12] In REDUCE-IT, serious bleeding was 2.7% against 2.1%, a difference that was not statistically significant.^[7] People who have heart disease or take heart medicines should ask a doctor or pharmacist first.^[4]

What is still unknown

The NIH Office of Dietary Supplements says the evidence is stronger for people who already have coronary heart disease than for healthy people.^[4] Benefit may also be larger in people who eat little fish: in VITAL, heart attacks fell by 40% in those who ate less than 1.5 servings a week.^[4] This is a result from one subgroup, so it is less certain than the main result of the trial.