Fish oil capsules contain two omega-3 fatty acids, eicosapentenoic acid (EPA) and docosahexenoic (DHA). Like aspirin, they make platelets in the blood less likely to stick together and may reduce inflammatory processes in the blood vessels.

Claims, purported benefits: Fish oil capsules prevent arrhythmias and other forms of heart disease, alleviate autoimmune disorders, and improve brain function and memory.

Bottom line: The omega-3 fatty acids in fish oil can help protect against cardiovascular disease in healthy people and in those who already have heart disease. Whether fish and fish oil supplements are good for the brain remains uncertain.

Healthy people are best off to get their omega-3s from fish—about 12 ounces a week. The following people should consider taking fish oil supplements, with their doctor’s approval: those who have coronary artery disease (1 gram a day of omega-3s on days when they don’t eat fish); those with high triglycerides (2 to 4 grams a day); those with rheumatoid arthritis, psoriasis, or other auto-immune disorders (3 grams a day).

Large doses of fish oil supplements have potential side effects that include nausea, diarrhea, belching, and a bad taste in the mouth. Large doses of fish oil can also increase the risk of hemorrhagic stroke, suppress the immune system, and decrease glucose control in people with diabetes.