Fish oil, also known as omega-3, is among the most popular dietary supplements. It’s often promoted to protect the heart, boost mood, reduce inflammation and support overall health.
But how much of this is backed by science, and when might fish oil supplements actually be worth taking?
A long history
People have been taking oils from fish for centuries.
Modern interest surged in the 1970s when scientists studying Inuit diets discovered omega-3 fatty acids and their heart-protective effects.
By the 1980s, fish oil capsules were being marketed as an easy way to get these healthy fats.
What’s in fish oil?
Fish oil comes from oily fish such as salmon, sardines, tuna, herring and mackerel. It’s rich in a special type of fat called omega-3 polyunsaturated fatty acids (PUFAs), mainly EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid).
These omega-3s play an important role in how our cells function. Every cell in the body is surrounded by a thin, flexible layer called a cell membrane. This membrane works like a protective skin: it keeps the cell’s contents safe, controls what moves in and out, and helps cells communicate with one another.
Omega-3s don’t build the membrane itself, but they slot into it, becoming part of its structure. This helps the membrane stay fluid and flexible, allowing it to work more efficiently, especially in tissue that relies on fast, precise signalling, such as in the brain and eyes.
Because we can’t make enough omega-3s on our own, we need to get them from food or, sometimes, supplements.
How are fish oil supplements made?
After fish are caught, their tissues are cooked and pressed to release oil. This crude oil is purified and refined to remove impurities including heavy metals such as copper, iron and mercury.
During processing, the oil may be concentrated to boost its EPA and DHA content.
The purified oil is then encapsulated in soft gels or bottled as liquid oil.
Some supplements are further treated to reduce odour or the familiar “fishy” aftertaste.
Fish oil and heart health
Omega-3 fatty acids are best known for their role in heart health, particularly for lowering triglycerides, a type of fat in the blood that, when elevated, can increase the risk of heart disease.
A 2023 paper pooled 90 clinical trials with more than 72,000 participants and found a near linear relationship between dose and effect. That doesn’t mean “more is always better”, but higher doses tended to produce bigger improvements in heart-related risk factors.
It found you need more than 2 grams per day of EPA and DHA combined to meaningfully lower triglycerides (by 15 to 30%). This is most relevant for people with existing heart disease, high triglycerides, or obesity.
But it’s important to read the label. A “1,000 mg” fish oil capsule usually refers to the total oil weight of the oil, not the active omega-3 content. Most standard capsules contain only about 300 mg of combined EPA and DHA the rest is other fats.
At lower doses, changes in blood fats were modest. The same analysis suggested low-dose fish oil may even nudge LDL or “bad” cholesterol up slightly, while having only a small effect on triglycerides.
A 2018 trial tested a high-strength purified EPA product (4 grams per day) in people already taking statins to lower their cholesterol. Over five years, it prevented one major heart event (heart attack, stroke or urgent procedure) for every 21 people treated. However this was a prescription-only pharmaceutical-grade EPA, not a standard fish-oil capsule.
In Australia, fish oils are sold in pharmacies, health food stores and supermarkets. Some concentrated products are available as “practitioner-only” supplements via health professionals.
The same purified EPA used in the 2018 trial is now available in Australia as Vazkepa, a prescription-only medicine. It was added to the Pharmaceutical Benefits Scheme (PBS) in October 2024, making it more accessible for high-risk patients.
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For otherwise healthy people, the evidence that standard fish oil supplements prevent heart attacks or strokes is much less convincing.
What about arthritis and joint pain?
Fish oil has mild anti-inflammatory effects.
In people with inflammatory arthritis (such as rheumatoid arthritis), omega-3s can reduce joint tenderness and morning stiffness.
These benefits, however, require higher consistent doses, usually around 2.7g of EPA and DHA per day. This is the equivalent of around nine standard 1,000mg fish oil capsules (containing 300 mg of EPA and DHA) daily for at least eight to 12 weeks.
Can fish oil improve mood?
Some studies suggest omega-3s, particularly those higher in EPA, can modestly reduce symptoms of clinical depression when taken alongside antidepressants.
A 2019 review of 26 trials (involving more than 2,000 people) found a small overall benefit, mainly for EPA-rich formulations at doses up to about 1 gram per day. DHA-only products didn’t show clear effects.
That doesn’t mean fish oil is a mood booster for everyone. For people without diagnosed depression, omega-3 supplements haven’t been shown to reliably lift mood or prevent depression.
How much can you take?
For most people, fish oil is safe.
Common side effects include a fishy aftertaste, mild nausea and diarrhoea. Taking capsules with food or choosing odourless or “de-fishified” products can help.
Prescription strength products such as Vazkepa (high-dose EPA) are also well tolerated, but they can slightly increase the risk of irregular heartbeat (atrial fibrillation) and bleeding.
Up to 3 grams per day of combined EPA and DHA from supplements is generally considered safe for most adults.
Higher doses for specific medical conditions should be taken under medical supervision.
So, should you take it?
The Heart Foundation recommends Australians eat two to three serves of oily fish a week. This would provide 250–500 mg of EPA and DHA per day.
If you don’t eat fish, a fish oil supplement (or algal oil if you’re vegetarian or vegan) can help you meet your omega-3 needs.
If you have heart disease (with high triglycerides) or inflammatory arthritis, fish oil may offer extra benefits. But dose and product type matter, so speak with a health professional.
For most people, though, two or three serves of oily fish each week remain the simplest, safest and most nutritious way to get omega-3s.
Mary Bushell is a Clinical Associate Professor in Pharmacy at the University of Canberra. Find Mary on X @mary_bushell
A version of this article was originally posted at Conversation and has been reposted here with permission. Any reposting should credit the original author and provide links to both the GLP and the original article. Find Conversation on X @ConversationUS
