The benefits of fish oil supplements include reducing triglyceride levels in people with high levels and reducing the risk of heart disease in people with healthy hearts, according to MedlinePlus. Fish oil contains omega-3 fatty acids, and these fatty acids reduce pain and swelling.
Fish oil prevents the blood from clotting too easily. Fish oil also seems effective in improving atherosclerosis in the coronary arteries but not in the carotid arteries, states MedlinePlus.
Other conditions for which fish oil supplements may be effective include age-related macular degeneration, asthma, bipolar disorder and psychosis, states MedlinePlus. Fish supplements also seem to slow weight loss in cancer patients and reduce the risk of endometrial cancer and heart failure in some patients. They may also improve symptoms in patients with Raynaud's syndrome and rheumatoid arthritis.
Fish oil supplements are not beneficial for patients with diabetes, pneumonia and migraines. Fish oil is a safe supplement if taken in doses of less than 3 grams, says MedlinePlus. Supplements carry the risk of side effects such as belching, nausea and bad breath.
Fish oil supplements should be used with caution when combined with certain hypertensive medications such as hydrochlorothiazide and furosemide, as low blood pressure may be the result, states MedlinePlus.