How to Choose a Fish Oil (Omega-3) Supplement
The big number on the front of a fish oil bottle is often not the number that matters. Here is how to read the label.
Last reviewed: October 2026 · How we research
Disclosure: As an Amazon Associate I earn from qualifying purchases. This guide is general information, not medical advice. Talk to your doctor before starting any supplement.
Look for EPA and DHA, not just "fish oil"
A label might say "1,000 mg fish oil" on the front, but the useful omega-3s are EPA and DHA. Turn the bottle around and add up the EPA and DHA per serving. That is the real amount you are getting, and it is often much lower than the front number. Plant oils such as flaxseed, canola and soybean oil supply a different omega-3 (ALA), and the body converts only small amounts of it into EPA and DHA.
Compare the forms
- Triglyceride form (rTG): Generally considered easier to absorb. Usually costs more.
- Ethyl ester: Common in less expensive products. Works, but it is usually better to take it with a meal that has some fat.
- Algae oil: A plant-based source of DHA (and sometimes EPA). Good for vegetarians and vegans, and it avoids fishy aftertaste for many people.
Purified, refined or distilled: why it matters
Fish take up contaminants such as mercury from the water, and larger predator fish tend to carry more. That is why the FDA sorts fish by mercury level and puts some species in a "choice to avoid" group. Supplements are a different story. The NIH Office of Dietary Supplements says omega-3 supplements have not been found to contain mercury, and it attributes this to the mercury being removed during processing and purification. That is a good reason to prefer an oil that is described as purified, refined or molecularly distilled over a crude or "unrefined" oil, unless the brand can show lab results for that batch.
One caution: words like "purified" and "distilled" are marketing terms, and a label alone cannot prove what is in the bottle. Look for independent testing (USP, NSF or IFOS) and for brands that publish a certificate of analysis, which is the lab report for a batch covering contaminants and freshness. If you would rather skip fish altogether, algae-based omega-3 comes from a different source entirely.
Allergens and soy
- Fish allergy. Fish oil comes from fish, and fish is one of the major food allergens. If you are allergic to fish, ask your allergist before using fish oil, and check the "Contains" line.
- Soy. Some softgels contain soy lecithin or soy-derived vitamin E. If you avoid soy, read "Other ingredients" and see our soy-free guide.
Freshness and quality
- Fish oil can go rancid. A strong, sour fish smell or taste, or burping with a bad aftertaste, is a warning sign.
- Look for products tested by an independent lab for purity and freshness, such as IFOS, USP, or NSF.
- Check the expiration date, and keep the bottle in a cool, dark place. Some people store it in the refrigerator.
- Look for sustainability labels such as MSC if that matters to you.
Practical tips
- Take it with a meal to improve absorption and reduce aftertaste.
- Enteric-coated or lemon-flavored versions can help if fishy burps are a problem.
- Eating fatty fish such as salmon, sardines or mackerel is another way to get omega-3s.
- The FDA advises getting no more than 5 grams a day of EPA and DHA combined from supplements.
- High doses of omega-3s may cause bleeding problems when combined with warfarin or other blood thinners, so ask your doctor before starting fish oil if you take them or have a medical condition.
Eating fish: what the US and Spain advise
Official advice about fish itself differs a little from country to country, but both single out high-mercury species.
- United States (FDA). "Best Choices" low in mercury include salmon, sardines, anchovies, Atlantic mackerel, cod, shrimp and canned light tuna. During pregnancy and breastfeeding the FDA suggests 2 to 3 servings a week from that list (a serving is about 4 ounces), and 2 servings a week for children, with smaller portions for younger ones.
- Spain. According to Spain's Ministry of Social Rights, Consumer Affairs and the 2030 Agenda, citing the food safety agency AESAN, pregnant and breastfeeding women and children under 3 should avoid swordfish, shark, bluefin tuna and pike. Children aged 3 to 12 should limit them to 50 grams a week, or 100 grams every two weeks.
Sources and further reading
We read these pages in October 2026. They come from government health agencies in the United States and Spain and are not affiliated with this site. Where official advice differs between countries, we say so in the guide. Always follow the advice of your own doctor or pharmacist.
- NIH Office of Dietary Supplements: Omega-3 Fatty Acids, consumer fact sheet (page dated July 2022)
- NIH Office of Dietary Supplements: Omega-3 Fatty Acids, health professional fact sheet (read October 2026)
- FDA: Advice About Eating Fish (read October 2026)
- Spain, Ministry of Social Rights, Consumer Affairs and the 2030 Agenda (recommendations from AESAN): fish consumption and mercury (in Spanish; read October 2026)
- FDA: Food Allergies (page dated March 2026)
- NIH Office of Dietary Supplements: Dietary Supplements, What You Need to Know (page dated January 2023)
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