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Fish Oil

By Melissa G. Marko, PhD, Senior Clinical Scientist, Nestle Nutrition ; Ara DerMarderosian, PhD, Professor Emeritus of Biology and Pharmacognosy, University of the Sciences

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Fish oil may be consumed by eating fish, extracted directly, or concentrated and put in capsule form. Active ingredients are omega-3 fatty acids (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]). Recently, genetically engineered yeast strains that can naturally produce substantial amounts of these oils have been engineered and are providing another source (1). Western diets typically are low in omega-3 fatty acids. (Other non-fish dietary sources of omega-3 fatty acids are walnuts and flaxseed oil.)


Fish oil is used for prevention and treatment of atherosclerotic cardiovascular disease, specifically by lowering triglyceride levels. Mechanisms are probably multiple but unknown. Benefits are suspected, but not yet supported, for primary prevention of atherosclerotic cardiovascular disease, lowering of cholesterol levels, treatment of rheumatoid arthritis, lowering blood pressure, and prevention of cyclosporine nephrotoxicity.


Strong evidence indicates that EPA/DHA (EPA plus DHA in various combinations) 800 to 1500 mg/day reduces risk of myocardial infarction and death due to arrhythmia in patients who have preexisting coronary artery disease and are taking conventional drugs (2). EPA/DHA also reduces triglycerides in a dose-dependent way (eg, 25 to 40% with EPA/DHA 4 g/day) and slightly lowers blood pressure (2 to 4 mm Hg with EPA/DHA > 3 g/day).

Adverse effects

Fishy eructation, nausea, and diarrhea may occur. Risk of bleeding increases with EPA/DHA > 3 g/day. Concerns about mercury contamination are not substantiated in laboratory testing. Even so, pregnant or breastfeeding women should not take omega-3 fatty acid supplements extracted from fish and should limit consumption of certain types and amounts of fish because of the potential risk of mercury contamination.

Drug interactions

Fish oil is contraindicated in patients on antihypertensives as it may lower blood pressure more than physiologically desired. Fish oil ingestion may increase the anticoagulant effect of warfarin, therefore patients taking warfarin should avoid fish oil (3).

Fish oil references

  • Xue Z, Sharpe PL, Hong SP, et al. Production of omega-3 eicosapentaenoic acid by metabolic engineering of Yarrowia lipolytica. Nat Biotechnol 31(8):734-740, 2013.

  • Agency for Healthcare Research and Quality. Effects of Omega-3 Fatty Acids on Lipids and Glycemic Control in Type II Diabetes and the Metabolic Syndrome and on Inflammatory Bowel Disease, Rheumatoid Arthritis, Renal Disease, Systemic Lupus Erythematosus, and Osteoporosis. AHRQ Publication No. 04-E012-1; 2004.

  • Buckley MS, Goff AD, Knapp WE. . Fish oil interaction with warfarin. Ann Pharmacother 38(1):50-52, 2004.