Favorable Efficacy (RCT)

Omega-3 (fish oil) for cardiovascular events

Omega-3 fatty acids (fish oil / EPA) vs. Placebo (oil capsule) · for Cardiovascular disease · real-time analysis of 7 studies · updated 2026-05-29

Whether fish oil prevents cardiovascular events depends heavily on the preparation and population. High-dose EPA-only trials (REDUCE-IT, JELIS) and the new hemodialysis trial (PISCES) show clear benefit, while low-dose or EPA+DHA combination trials (VITAL, ASCEND, STRENGTH) are essentially null. A pooled average therefore hides more than it reveals.

Efficacy (RCT): Efficacy evidence on clinical outcomes. Effects are risk ratios with number-needed-to-treat where a baseline risk is available. Glossary →

Interpretation & tips

Don't read the pooled diamond as the answer—the heterogeneity is the point. Benefit tracks high-dose EPA-only formulations (REDUCE-IT, JELIS) and the hemodialysis PISCES trial; ~1 g/day or EPA+DHA trials (VITAL, ASCEND, STRENGTH) were null. Comparator oils, open-label designs, and differing endpoints further confound. PISCES's headline was a recurrent-events analysis, not first-event.

14% lower risk of major cardiovascular events

Pooled RR 0.86 (95% CI 0.78–0.95) across 7 studies, 93,805 patients (random-effects, I² 81%).

0.86

Pooled RR

0.78–0.95

95% CI

Studies

93,805

Patients

NNT

Forest plot—Major cardiovascular events

Study results—Major cardiovascular events

Study	Design	Dose / regimen	Treatment	Control	RR [95% CI]	Improvement	NNT	Weight
PISCES (Lok) 2026 note	DB-RCT	Fish oil 4 g/day (1.6 g EPA + 0.8 g DHA)	127/610	208/618	0.62 [0.51–0.75]	38%	8	11%
STRENGTH (Nicholls) 2020 note	DB-RCT	Omega-3 carboxylic acid (EPA+DHA) 4 g/day	785/6539	795/6539	0.99 [0.90–1.08]	1%	654	16%
REDUCE-IT (Bhatt) 2019 note	DB-RCT	Icosapent ethyl (EPA) 4 g/day	705/4089	901/4090	0.78 [0.72–0.86]	22%	21	16%
VITAL (Manson) 2019 note	DB-RCT	Marine n-3 (EPA+DHA) 1 g/day	—	—	0.92 [0.80–1.06] ~	8%	386	13%
ASCEND 2018 note	DB-RCT	n-3 (EPA+DHA) 1 g/day	689/7740	712/7740	0.97 [0.88–1.07]	3%	337	16%
JELIS (Yokoyama) 2007 note	RCT	Purified EPA 1.8 g/day + statin	262/9326	324/9319	0.81 [0.69–0.95]	19%	150	12%
GISSI-Prevenzione 1999 note	RCT	n-3 PUFA ~1 g/day	—	—	0.90 [0.82–0.99]	10%	—	16%

RR < 1 favors treatment for outcomes where lower is better. Rows in gray have a confidence interval crossing 1 (individually inconclusive). “~” marks effects reported as OR/HR and treated as RR-approximations. “excl” = excluded from pooling (e.g. reviews).

Notes & interpretation

PISCES (Lok) 2026—Participants with ≥1 serious cardiovascular event. Headline primary (recurrent events) was HR 0.57 (0.47-0.70). Only dialysis trial here; serious bleeding was lower with fish oil (4.8% vs 7.6%).
STRENGTH (Nicholls) 2020—Null (HR 0.99, 0.90-1.09). Same 4 g/day dose as REDUCE-IT but EPA+DHA—the key contrast.
REDUCE-IT (Bhatt) 2019—Positive. Published HR 0.75 (0.68-0.83). Mineral-oil comparator raised LDL/CRP in controls (debated).
VITAL (Manson) 2019—Null for the primary composite (MI/stroke/CV death); MI alone was lower (HR 0.72, 0.59-0.90).
ASCEND 2018—Null. Published rate ratio 0.97 (0.87-1.08).
JELIS (Yokoyama) 2007—Positive. Published HR 0.81 (0.69-0.95). Open-label (PROBE) design; high-fish-intake population.
GISSI-Prevenzione 1999—Modestly positive. RR from reported relative risk reduction ~10% (two-way analysis); per-arm counts not confirmed. Open-label.

Background

Large randomized trials of marine omega-3 fatty acids for cardiovascular prevention have produced famously divergent results, differing in formulation (EPA vs EPA+DHA), dose (~1 vs 4 g/day), comparator oil, and population. PISCES (2026) tested 4 g/day fish oil in hemodialysis patients.

Topic methodology & caveats

Risk ratios from each trial's participant-level primary-event counts (2×2) where available, else the reported hazard or relative-risk ratio. Pooling is shown for completeness only; formulation, dose, population, and comparator differences make it of little interpretive value.