Eicosapentaenoic acid (EPA) is an omega-3 oil found primarily in cold-water fish such as salmon, mackerel, sardines, herring, cod, tuna, and anchovies. The oil belongs to a class of nutrients known as essential fatty acids, which are fats that are required by the body for normal biological functions but cannot be manufactured by the body, and therefore must be provided by the diet. While isolated EPA is available as an individual supplement, the oil is most commonly found in the form of fish oil, which contains high concentrations of EPA and another omega-3 essential fatty acid, DHA (docosahexaenoic acid). Cod liver oil is also a rich source of EPA and DHA, along with the fat-soluble vitamins A and D.
Dosage recommendations for EPA vary with intended application. Studies on lupus patients have used as much as 20 grams of fish oil per day with no signs of toxicity. Side effects such as belching, "fishy" breath, and diarrhea have been reported with high doses of fish oil; however, these effects can be reduced by the use of time-release formulations.