Fish oil

Can fish oil cause atrial fibrillation?

Updated 4 Nov 2026

Short answer

At high doses in people at high heart risk, it can. A 2026 review of 35 trials and 114,592 people found 43% higher odds with more than 1.5 g a day in this group, an extra 0.8 cases per 100 people.[1] It found no significant rise at lower doses or in lower-risk people.[1]

What the studies found

Atrial fibrillation is an irregular heartbeat. A 2026 review included 35 trials and 114,592 people aged 50 or older, who took at least 500 mg of EPA and DHA a day for at least 12 months.[1] It split the trials by dose and by heart risk:[1]

  • high heart risk, more than 1.5 g a day: odds ratio 1.43, a significant rise[1]
  • high heart risk, lower dose: odds ratio 1.07, not significant[1]
  • low heart risk, more than 1.5 g a day: odds ratio 1.03, not significant[1]
  • low heart risk, lower dose: odds ratio 1.06, not significant[1]

The absolute difference in the high-risk, high-dose group was 0.8%, or about 8 extra cases per 1,000 people.[1]

Single trials point the same way. In REDUCE-IT, 3.1% of people on 4 g a day of purified EPA went to hospital for atrial fibrillation or flutter, against 2.1% on placebo.[2] The STRENGTH trial also found more atrial fibrillation at 4 g a day of an EPA and DHA product.[3]

Where the sources disagree

Earlier reviews with fewer trials found a broader risk. One review of 8 trials found 24% higher risk overall, or 4.0% against 3.3%. It found about 12% more at about 1 g a day and about 50% more at 1.8 to 4 g.[4] Another review of 15 trials found 25% more.[5] The newer review had many more trials and found no rise at lower doses.[1]

The 2020 Cochrane review found no change in arrhythmia as a whole, with low-certainty evidence.[6]

Fish in the diet shows a different pattern. Observational studies linked higher intake or blood levels of omega-3 to lower risk of atrial fibrillation, with the largest fall at about 650 mg a day from food.[4] Studies of this kind cannot prove cause and effect.[3]

Why it may happen

The cause is not proven. One review suggests that omega-3 fats raise vagal tone, the activity of the nerve that slows the heart, and that the effect depends on the dose.[4] In experiments, low vagal stimulation lowered the risk of atrial fibrillation, and high stimulation raised it.[4]

Who should be careful

The risk showed mainly in people with heart disease or a high risk of it who took high doses.[1] A typical 1000 mg capsule holds about 300 mg of EPA and DHA, so 1.5 g is about five such capsules.[3] People with heart disease, or who already have an irregular heartbeat, should ask a doctor or pharmacist before they take fish oil.[3][1]

What is still unknown

The authors of the 2026 review call for new studies that weigh this risk against possible benefits of high doses.[1] The authors chose the 1.5 g cut-off when they split the trials, so it is not a proven safe limit.[1]

Sources (6)

  1. Effects of Omega-3 Fatty Acid Treatment on Risk for Atrial Fibrillation: An Updated Meta-Analysis of 35 Trials including 114 592 Individuals. Abuknesha NR, O'Keefe JH, Qian F, Tintle NL, Lin Y, Sun Y, et al. Circ Arrhythm Electrophysiol, 2026. PMID 42517224
  2. Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia. Bhatt DL, Steg PG, Miller M, Brinton EA, Jacobson TA, Ketchum SB, et al. N Engl J Med, 2019. PMID 30415628
  3. Omega-3 Fatty Acids: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov
  4. Omega-3 and Risk of atrial fibrillation: Vagally-mediated double-edged sword. O'Keefe EL, O'Keefe JH, Abuissa H, Metzinger M, Murray E, Franco G, et al. Prog Cardiovasc Dis, 2025. PMID 39617283
  5. Efficacy and Safety of Omega-3 Fatty Acids in the Prevention of Cardiovascular Disease: A Systematic Review and Meta-analysis. Yan J, Liu M, Yang D, Zhang Y, An F Cardiovasc Drugs Ther, 2024. PMID 36103100
  6. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Abdelhamid AS, Brown TJ, Brainard JS, Biswas P, Thorpe GC, Moore HJ, et al. Cochrane Database Syst Rev, 2020. PMID 32114706

More about fish oil

What is fish oil?Does fish oil reduce inflammation?How much EPA and DHA is in a fish oil capsule?Is eating fish better than taking fish oil?What is fish oil used for?Should fish oil be taken with food?

For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.