What is fish oil (omega-3) good for?
Last updated: June 2026 · Reviewed by the FactoWiki Editorial Team for clarity and source accuracy
The real evidence for omega-3 on triglycerides, heart, dry eye and mood — and how to judge quality.
Key takeaways
- Omega-3's strongest evidence is lowering high triglycerides; EPA/DHA dose matters more than 'fish oil' mg.
- Routine fish-oil-for-heart-prevention claims are weaker than assumed; mood and dry-eye uses are modest.
- Choose fresh, third-party-tested oil; it can thin the blood, so check before surgery or with blood thinners.
What omega-3 and fish oil are
Omega-3s are a family of essential fats, the most important being EPA and DHA, found mainly in oily fish. Fish oil supplements concentrate these, and there's a vegan alternative from algae. They're among the most-studied supplements, with a mix of genuinely strong evidence for some uses and disappointing results for others — so the useful question is which specific benefit you're after.
Triglycerides: the strongest evidence
Omega-3's clearest effect is lowering high triglycerides, a type of blood fat. The effect is reliable and dose-dependent, and prescription-strength omega-3 is actually used medically for very high triglycerides. Over-the-counter fish oil can help here too, but usually at higher doses than a single small capsule provides — so the amount of EPA and DHA on the label, not just 'fish oil', is what matters.
Heart, brain and mood
For preventing heart attacks and strokes in the general population, large trials have been mixed and often underwhelming, so the routine 'fish oil for heart health' claim is weaker than people assume. There's some evidence for omega-3 in depression (particularly EPA-heavy formulas) and ongoing research in brain health, but these are more modest and less settled than the triglyceride effect.
Dry eye, joints and pregnancy
Omega-3 has some evidence for easing dry-eye symptoms and for modestly reducing joint stiffness in inflammatory arthritis. DHA is also important in pregnancy for fetal development, which is why it's often recommended then (from a low-mercury source). These are reasonable, if secondary, uses — again depending on getting an adequate EPA/DHA dose rather than just any fish oil.
Quality, freshness and safety
Quality varies a lot. Fish oil can oxidise (go rancid), which is unpleasant and counterproductive, so freshness and reputable brands matter; third-party testing also screens for contaminants like mercury and PCBs. The main safety point is that omega-3 can mildly thin the blood, so people on blood thinners or facing surgery should check with a doctor. Fishy burps are common and can be reduced by taking it with meals or choosing enteric-coated forms.
A sensible approach
If your goal is lowering high triglycerides, omega-3 is genuinely useful — at an adequate EPA/DHA dose, ideally guided by a doctor. For general 'heart health' in someone with no specific issue, eating oily fish a couple of times a week is a reasonable, food-first approach. Either way, judge a product by its actual EPA and DHA content and its freshness, not by the size of the 'fish oil' number on the front.
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Frequently asked questions
What is fish oil good for?
Its strongest evidence is lowering high triglycerides; it has more modest evidence for dry eye, joints and mood.
Does fish oil prevent heart attacks?
Large trials are mixed, so routine heart-prevention claims are weaker than assumed — eating oily fish is a reasonable food-first approach.
How do I judge a fish oil's quality?
Check the EPA and DHA content (not just total fish oil), choose fresh, third-party-tested products, and store them well.
Is fish oil safe?
Generally yes, but it can mildly thin the blood — check with a doctor if you take blood thinners or have surgery coming up.
This article is general information, not medical advice. See our medical disclaimer, and talk to a qualified healthcare professional about your own situation.