Is 1,000 mg of fish oil the same as 1,000 mg of omega-3?

No, and the difference is usually large. The front-label figure is the weight of the oil; the EPA and DHA lines on the Supplement Facts panel tell you how much omega-3 it contains. A 2,000 mg serving commonly provides about 600 mg of EPA plus DHA.

Does fish oil prevent heart attacks?

In the general population, the evidence says no. The VITAL trial followed 25,871 adults taking 1 g daily and found no significant reduction in major cardiovascular events. A benefit was found in REDUCE-IT, but that used a prescription-only purified EPA product at 4 g daily in statin-treated patients with elevated triglycerides — a different product, dose and population.

How much EPA and DHA do I actually need?

General guidance is roughly 250 to 500 mg combined per day, which one to two servings of oily fish weekly broadly covers. The triglyceride-lowering dose is far higher, around 2 to 4 g, and belongs under medical supervision rather than self-selection.

Is krill oil better than fish oil?

Krill oil is often marketed on better absorption, but it typically contains considerably less EPA and DHA per capsule and costs more. Compare the EPA and DHA amounts per serving and the price of reaching your target from each, rather than comparing the claims.

Can I take fish oil before surgery?

Raise it with your surgeon. Omega-3s have a mild antiplatelet effect, and supplements are commonly stopped one to two weeks before a procedure. The same caution applies alongside anticoagulant or antiplatelet medication.

Omega-3 (EPA and DHA): evidence, dosage and safety

What is Omega-3 (EPA and DHA)?

Omega-3 is a family of polyunsaturated fats. The two that matter clinically are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), found in oily fish such as salmon, sardines and mackerel, and in algae, which is where the fish get them. A third, ALA, comes from plant sources like flaxseed and converts to EPA and DHA only inefficiently in humans, so an ALA product is not a substitute. Supplements are sold as fish oil, krill oil, cod liver oil or algal oil, and they differ substantially in how much actual EPA and DHA they deliver per capsule.

How it works

EPA and DHA are incorporated into cell membranes, where they influence membrane fluidity and act as precursors to signalling molecules involved in resolving inflammation. DHA is structurally important in the brain and retina. In the liver, they reduce production of very-low-density lipoprotein, which is the mechanism behind the well-established triglyceride reduction. They also have a mild antiplatelet effect, which is the basis of the bleeding caution rather than a benefit to seek.

What the research actually shows

Evidence strength varies by what is being claimed, so each use is graded separately against the published criteria rather than averaged into one reassuring letter.

For lowering triglycerides

AStrong evidence

This is the established clinical use and it is not in serious dispute. High doses, generally around 2 to 4 g of combined EPA and DHA daily, reliably reduce triglycerides, with larger reductions in people whose levels start higher. Prescription omega-3 preparations exist specifically for this indication. Note the dose: this is several times what a typical one-capsule supplement serving provides.

For preventing heart disease or cancer in the general population

DWeak evidence

The VITAL trial randomised 25,871 adults to 1 g of omega-3 daily or placebo and found no significant reduction in major cardiovascular events or invasive cancer over roughly five years. This is a large, well-conducted trial in a generally healthy population, and it directly contradicts how most fish oil is marketed. Observational associations between eating fish and better cardiovascular outcomes remain, but they have not transferred to supplements in people who are not deficient or high-risk.

Sources: Manson JE, Cook NR, Lee I-M, et al

For high-risk patients already on statins

BModerate evidence

This is a genuine exception worth stating precisely. REDUCE-IT randomised 8,179 statin-treated patients with elevated triglycerides to 4 g daily of icosapent ethyl — a purified, prescription-only ethyl ester of EPA — and found a significant reduction in cardiovascular events. That result belongs to a specific prescription product at a specific dose in a specific high-risk group. It is not evidence for an over-the-counter fish oil capsule, and a separate trial of a different omega-3 preparation did not replicate the benefit.

Sources: Bhatt DL, Steg PG, Miller M, et al

For memory and cognitive function

DWeak evidence

DHA is structurally important in the brain, which makes the claim plausible and keeps it in circulation. Trials of supplementation for cognitive performance or prevention of decline in older adults have been largely disappointing and inconsistent. Structural importance is not the same as benefit from adding more once intake is adequate.

For joint pain in rheumatoid arthritis

BModerate evidence

Among the inflammatory claims, this one has the most support. Trials report modest reductions in joint tenderness and morning stiffness, generally at higher doses taken over months. The effect is real but modest, and it is an adjunct to treatment rather than a replacement for it.

Effective dosage

General intake guidance is usually expressed as roughly 250 to 500 mg of combined EPA and DHA daily, which one to two servings of oily fish per week broadly covers. The triglyceride-lowering effect requires far more — around 2 to 4 g of combined EPA and DHA daily, which is a clinical dose rather than a maintenance one and warrants medical supervision. The important habit is to read the EPA and DHA lines on the Supplement Facts panel and ignore the fish oil total on the front.

Where products diverge from the research. This category has the widest gap between the front label and the panel of anything on this site. A product advertising 1,000 mg per softgel is quoting the weight of the oil, not the omega-3 in it. A two-softgel serving of 2,000 mg fish oil commonly provides around 600 mg of EPA plus DHA — roughly 30 per cent, with the rest being other fats. Someone aiming for a 2 g therapeutic dose from that product would need six or seven softgels, not two. Concentrated products exist that deliver far more per capsule, and they can only be identified by comparing the EPA and DHA lines.

Safety, side effects and interactions

Omega-3s have a mild antiplatelet effect, so they can increase bleeding risk, which matters for anyone taking an anticoagulant or antiplatelet drug and for anyone with surgery scheduled — supplements are commonly stopped a week or two beforehand. Fish-derived products are unsuitable for anyone with a fish or shellfish allergy; algal oil is the alternative. Common side effects are fishy aftertaste, belching and gastrointestinal upset, which taking capsules with food or frozen can reduce. Cod liver oil is a separate caution: it contains vitamin A, which accumulates and can reach harmful levels, so it should not be dosed as though it were plain fish oil. Oils oxidise, and a rancid product is both unpleasant and less useful; check expiry dates and store as directed. Doses above about 3 g daily from supplements are generally a matter for a clinician rather than self-selection.

None of this is medical advice. See the medical disclaimer for what that means before you act on anything here.

Omega-3 (EPA and DHA)

What is Omega-3 (EPA and DHA)?

How it works

What the research actually shows

For lowering triglycerides

For preventing heart disease or cancer in the general population

For high-risk patients already on statins

For memory and cognitive function

For joint pain in rheumatoid arthritis

Effective dosage

Safety, side effects and interactions

Products we have covered containing Omega-3 (EPA and DHA)

NOW Omega-3 Molecularly Distilled

Common questions

References

Related ingredients