Evidence

Research on the use of fish oil for specific conditions shows:

• Heart disease. While research shows that people who eat dietary sources of fish oil at least twice a week have a lower risk of dying of heart disease, taking fish oil supplements seems to have little to no benefits to heart health.
• High blood pressure. Multiple studies report modest reductions in blood pressure in people who take fish oil supplements. There's some evidence that the beneficial effects of fish oil might be greater for people with moderate to severe high blood pressure than for those with mild blood pressure elevation.
• High triglycerides and cholesterol. There's strong evidence that omega-3 fatty acids can significantly reduce blood triglyceride levels. There also appears to be a slight improvement in high-density lipoprotein (HDL, or "good") cholesterol, although an increase in levels of low-density lipoprotein (LDL, or "bad") cholesterol also was observed.
• Rheumatoid arthritis. Studies suggest fish oil supplements might help reduce pain, improve morning stiffness and relieve joint tenderness in people with rheumatoid arthritis. While relief is often modest, it might be enough to reduce the need for anti-inflammatory medications.