Medically reviewed on October 24, 2017
Fish oil is a dietary source of omega-3 fatty acids — substances your body needs for many functions, from muscle activity to cell growth.
Omega-3 fatty acids are derived from food. They can't be manufactured in the body. Fish oil contains two omega-3s called docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Dietary sources of DHA and EPA are fatty fish, such as salmon, mackerel and trout, and shellfish, such as mussels, oysters and crabs. Some nuts, seeds and vegetable oils contain another omega-3 called alpha-linolenic acid (ALA).
Fish oil supplements come in liquid, capsule and pill form.
People take fish oil to reduce the risk of heart attacks and strokes, to treat high triglycerides and high blood pressure, and to improve symptoms of rheumatoid arthritis.
Research on the use of fish oil for specific conditions shows:
- Heart disease. Research shows that eating dietary sources of fish oil — such as tuna or salmon — twice a week is associated with a reduced risk of developing heart disease. Taking fish oil supplements for at least six months has been shown to reduce the risk of heart-related events (such as heart attack) and death in people who are at high risk of heart disease. Research also suggests that the risk of congestive heart failure is lower in older adults who have higher levels of EPA fatty acids.
- High blood pressure. Multiple studies report modest reductions in blood pressure in people who take fish oil supplements. There's some evidence that this effect is greater for people with moderate to severe hypertension than those with mild hypertension.
- 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.
Omega-3 fatty acids are essential for good health. Try to get them from your diet by eating fish — broiled or baked, not fried. Fish oil supplements might be helpful if you have cardiovascular disease or an autoimmune disorder. Fish oil also appears to contain almost no mercury, which can be a cause for concern in certain types of fish. While generally safe, too much fish oil can increase your risk of bleeding and might suppress your immune response. Take fish oil supplements under a doctor's supervision.
Safety and side effects
When taken as recommended, fish oil supplements are generally considered safe.
However, fish oil supplements can cause:
- A fishy aftertaste
- Bad breath
- Loose stools
Taking high doses of fish oil supplements might increase the risk of bleeding and possibly increase the risk of stroke.
It's unclear whether people with fish or shellfish allergies can safely take fish oil.
Possible interactions include:
- Anticoagulant and anti-platelet drugs, herbs and supplements. These types of drugs, herbs and supplements reduce blood clotting. It's possible that taking fish oil supplements with them might increase the risk of bleeding.
- Blood pressure drugs, herbs and supplements. Taking fish oil supplements might slightly lower blood pressure. Taking these supplements with blood pressure drugs might increase the effects on blood pressure.
- Contraceptive drugs. Some contraceptive drugs might interfere with the effect fish oil typically has on triglycerides.
- Orlistat (Xenical, Alli). Taking fish oil with this weight-loss drug might decrease absorption of fish oil fatty acids. Consider taking the supplement and drug two hours apart.
- Vitamin E. Taking fish oil can reduce vitamin E levels.