Fish Oil and Omega-3

Omega-3 and fish oil are used interchangeably on labels and in search, and they do not mean the same thing. NCCIH describes omega-3s as a kind of fat found in foods and in the human body. Fish oil is one supplement that supplies two of them. The distinction decides what you are actually buying.

Is omega-3 the same as fish oil?

No. Omega-3 is the class of fat; fish oil is one source of it.

NCCIH lists three main types of omega-3. EPA and DHA come from seafood — NCCIH names cold-water fish such as salmon, mackerel and tuna, along with shellfish — and from fish oil supplements. ALA — alpha-linolenic acid — is found in plant oils such as flaxseed, soybean and canola, and in plant foods including chia seeds and walnuts.

So a flaxseed oil capsule supplies omega-3 and contains no fish oil at all. The two words are not substitutes.

What are the different omega-3 supplements?

NCCIH lists several, and they differ in which omega-3 they carry:

• Fish oil — EPA and DHA.
• Fish liver oil, including cod liver oil — EPA and DHA, plus vitamins A and D.
• Krill oil — EPA and DHA in a phospholipid form.
• Algal oils — a vegetarian source of DHA.
• Flaxseed oil — ALA, not EPA or DHA.

Anyone avoiding fish for dietary or ethical reasons is choosing between algal oil, which supplies DHA directly, and flaxseed oil, which supplies ALA. NCCIH presents these as different products, not as interchangeable ones.

What does the evidence show for omega-3?

NCCIH’s summaries, condition by condition:

• Triglycerides. A 2020 review of 23 studies showed EPA and DHA reduce triglycerides by about 15 percent. This is the clearest positive finding on the page.
• Heart disease. A 2020 review of 86 studies found omega-3s slightly reduced the risk of coronary events and coronary death, and a 2019 analysis concluded 1 gram a day provides some benefits to cardiovascular health.
• Stroke. A 2020 review found supplements had little or no effect. Higher doses showed some signal, but NCCIH notes only two studies used doses that high.
• Rheumatoid arthritis. A 2022 review found omega-3-rich diets may improve symptoms such as pain and swollen, tender joints; a 2021 review noted benefit but judged the evidence low.
• Depression. A 2021 review concluded any effect may be too small to be meaningful, with evidence quality judged low or very low.
• ADHD. A 2023 review of 36 studies found no evidence that symptoms are likely to improve.
• Cognitive decline. A 2022 review suggests a possible protective effect in people without dementia, and no effect on cognition in people already diagnosed with Alzheimer’s disease.
• Eye conditions. For age-related macular degeneration, no additional benefit beyond other supplements. For dry eye, a 2022 review suggested symptoms may improve, while a large 2018 NIH-sponsored trial found supplements no more helpful than placebo.

The pattern is a modest, reasonably supported effect on triglycerides, a small cardiovascular signal, and a long list of conditions where the finding is mixed, small, or absent.

What are the side effects of fish oil?

NCCIH describes side effects as usually mild: unpleasant taste, bad breath, bad-smelling sweat, headache, and gastrointestinal symptoms such as heartburn, nausea and diarrhoea.

This NCCIH page does not name drug interactions and does not set an upper limit. It references 1 gram a day in the cardiovascular studies and describes three or more capsules a day as a high dose in the stroke research, but those are descriptions of study protocols, not recommended amounts. Anyone on an anticoagulant has an obvious reason to raise fish oil with their prescriber; this source does not settle that question either way.