Make sure that the supplement provides the amount of omega-3 fatty acids that your doctor suggests. Supplements frequently supply 180 milligrams (mg) of eicosapentaenoic acid (EPA) and 120 mg of docosahexaenoic acid (DHA) -- the two main omega-3 fatty acids found in fish.
Check that the manufacturer's address is on the label -- and, ideally, an e-mail or phone number, too -- so that you can get in touch if you have questions or concerns. Also check that the company certifies that the product is free of environmental pollutants like mercury, pesticides and dioxins, which may be present in some fish. Avoid products that carry phrases on the label indicating they are miracle cures, medical breakthroughs or other unsubstantiated claims.