Whether a fish oil capsule does anything depends on whether you already have heart disease. If you do, there is a prescription version with a real result behind it. If you don't, the trials show very little. Those are two different answers to what sounds like one question, which is why the advice on this contradicts itself depending on where you read it.
If you don't have heart disease
The biggest review on this is a Cochrane one, 86 trials and 162,796 people. It looked at long-chain omega-3 supplements, meaning the two fats in a fish oil capsule, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). It found little or no effect on deaths from any cause and little or no effect on cardiovascular events. Both of those findings were rated high certainty, which means further trials are unlikely to change the answer.
There was a possible small reduction in coronary events and deaths, but the certainty was low and the effect was small. It worked out at 167 people taking a capsule every day to prevent one event. Which is another way of saying the other 166 got nothing from it.
One thing did move. Triglycerides, a type of fat in your blood that goes up with weight, alcohol and refined carbohydrates, fell by around 15%, and that was rated high certainty.
That is a genuine change and it is also a useful lesson. A number on a blood test moving in the right direction is not the same as fewer heart attacks, and in these trials it did not translate into fewer events. Which is why the thing to look for in any study is what happened to people, not what happened to their numbers.
The Heart Foundation's position matches this. They don't recommend routine fish oil supplements for people without heart disease, and say eating fish is the way to get these nutrients.
Put simply: if you are generally well and taking fish oil to look after your heart, the evidence does not back it. The same money spent on tinned fish does more.
If you do have heart disease, it's a different question
In a 2018 trial, a prescription purified EPA at 4g a day, given to people already taking a cholesterol-lowering statin and with raised triglycerides, prevented one major cardiovascular event for every 21 people treated over about five years.
In Australia that product is Vazkepa, and it was added to the Pharmaceutical Benefits Scheme in October 2024. It's prescription-only, and at 4g a day it is roughly four times the omega-3 most people get from a supermarket bottle, and more than ten times what is in a single capsule.
This is also still argued about. A near-identical trial using a different omega-3 formulation found no benefit at all, and the first trial used mineral oil as its dummy capsule. Mineral oil may itself nudge cholesterol and inflammation upward, so the comparison group might have got slightly worse rather than the treatment group getting better. Some cardiologists think that is what flattered the result. It isn't settled.
Atrial fibrillation, the one real safety question
Atrial fibrillation is an irregular heartbeat. It is not usually an emergency, but it raises the risk of stroke and it needs treating, so it is the side effect to know about with fish oil.
The risk is tied to the dose. Across the trials it turns up in people taking more than about 1,500mg of EPA and DHA a day, and most of all in people who already have heart disease. Below that, no increase has been found. Supermarket capsules sit well under it. The analysis that drew that line was funded by an omega-3 industry body, so the 1,500mg mark is not as firm as it sounds.
At the prescription dose, the regulators have already acted. In 2023 the European medicines regulator added atrial fibrillation to the product information for prescription omega-3 medicines as a common side effect, noted the risk is highest at 4g a day, and said the medicine should be stopped permanently if it develops. Another reason that version belongs with a doctor rather than on a shelf.
How to read your own bottle
If you have a bottle in the cupboard, this is the one thing to do with it. Turn it over, find EPA and DHA on the ingredients panel, add those two numbers together, and multiply by the number of capsules you take a day. That is your actual daily dose.
The big number on the front of the bottle is usually the weight of the fish oil, not the omega-3 in it. A 1,000mg fish oil capsule commonly contains around 300mg of EPA and DHA combined. So three capsules a day, which sounds like 3g, is closer to 900mg.
That matters because the triglyceride effect in the trials needed somewhere above 2g a day of combined EPA and DHA. The dose on most shelves and the dose in the trials are rarely the same thing.
The numbers to aim at from food
2 to 3 serves of fish a week, with at least one of them oily. A serve is 100g cooked, which is roughly the size of your palm. That covers the Heart Foundation's target of 250 to 500mg of marine omega-3 a day.
Plus about 1g a day of plant omega-3, alpha-linolenic acid (ALA). That is a small handful of walnuts, or 2 to 3 teaspoons of ground linseed or chia, or a tablespoon of canola oil.
Tinned counts. Tinned fish carries as much long-chain omega-3 as fresh, costs a fraction, and keeps in the cupboard. Wild-caught salmon, sardines and mackerel are the ones to look for. Tuna has far less than the other three.
Where the fish evidence is weaker
The trial evidence for eating fish is thinner than the trial evidence for capsules, simply because most trials handed out capsules. The recommendation to eat fish leans partly on observational research, which follows people who already eat a lot of fish and finds they have less heart disease. The catch with that kind of study is that fish eaters tend to differ in other ways too, so you can never fully separate the fish from everything else about them. It is weaker evidence than a trial, and that is where it stands.
What the capsule trials do establish is that the isolated version hasn't reproduced the benefit in people who are otherwise well. Nutrition has been here before. Beta-carotene and vitamin E both looked protective in people who ate more of them, and both failed to protect anyone once they were put in a capsule and trialled.
If you already take it
Nothing here is a reason to tip out a bottle you have already bought. Supermarket and pharmacy capsules usually sit somewhere between 300mg and 1,000mg of combined EPA and DHA a day, and at those doses the evidence does not show harm. It shows very little of anything.
One thing I would push back on is continuing because it feels like it is working. You cannot feel your cardiovascular risk, so for that purpose there is nothing to notice either way, in either direction. If you take fish oil for joint pain, dry eyes or mood, those are separate questions with their own evidence, and a fair conversation to have with your GP. If you take it for your heart and you don't have heart disease, the capsule is not doing what the packet implies.
There's two situations where it stops being a neutral decision. If you are taking more than 1,500mg a day, raise it with your GP, for the reason above. And if you are on a blood thinner or have surgery coming up, tell whoever is prescribing that you take fish oil.
If this is you
If you have heart disease, high triglycerides or a family history that worries you, this is a conversation with your GP rather than a decision to make in the supplement aisle. The version with evidence behind it is prescribed.
Where Greenher fits
It doesn't. Greenher Daily has no omega-3 in it, and this isn't a gap a greens powder fills. You get omega-3 from food, and the cheapest sources are tinned fish and a tablespoon of linseed.
The takeaway
Whether fish oil does anything depends on whether you have heart disease. Without it, the trials show little or nothing. With it, there is a prescription version at 4g a day with a real result behind it. Check your own bottle by adding the EPA and DHA and multiplying by the capsules you take a day, and aim for 2 to 3 serves of fish a week instead.
About this series
This post is part of Is This Just Getting Older?, a collaboration running through October with eight of us working with women in health, performance and wellbeing. Menopause, nutrition, fibre, snacks, movement, energy, self-compassion and sleep, one topic at a time, leading up to World Menopause Day on 18 October.
There is a Midlife Health and Wellbeing Pack being given away across the campaign, worth more than $3,000, with consultations, books, coaching sessions and a month of Greenher Daily in it.
To enter: follow all eight of us, then like the giveaway post and leave a comment saying one thing you wish more people understood about midlife health. Every account and the post are on one page here. Entries close 18 October.
The science behind this post:
- Abdelhamid AS, Brown TJ, Brainard JS, et al. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews. 2020;3:CD003177. Evidence current to February 2019. cochranelibrary.com
- Gencer B, Djousse L, Al-Ramady OT, et al. Effect of long-term marine omega-3 fatty acids supplementation on the risk of atrial fibrillation in randomized controlled trials of cardiovascular outcomes. Circulation. 2021;144(25):1981-1990. ahajournals.org
- Bhatt DL, Steg PG, Miller M, et al. Cardiovascular risk reduction with icosapent ethyl for hypertriglyceridemia (REDUCE-IT). New England Journal of Medicine. 2019;380(1):11-22.
- Harris WS, O'Keefe JH, et al. Effects of omega-3 fatty acid treatment on risk for atrial fibrillation. An updated meta-analysis of 34 trials including 114,326 individuals. 2025. Supported by the Global Organization for EPA and DHA. Read the analysis
- European Medicines Agency, Pharmacovigilance Risk Assessment Committee. Meeting highlights, 25 to 28 September 2023. Atrial fibrillation added as a common side effect of omega-3-acid ethyl ester medicines. ema.europa.eu
- Heart Foundation (Australia). Omega-3, omega-6 and heart health. Serve sizes and daily targets for marine and plant omega-3. heartfoundation.org.au