Optimal treatments for depression must be safe and effective, with ideal treatments also providing other health benefits as well. Omega-3 fatty acids are nutritional compounds with widely established health benefits. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are omega-3 fatty acids found in fish and marine sources. Mood disorder studies have supported a role for omega-3 fatty acids in the treatment of depression. In a study from 1998, it was demonstrated in a cross-national study that the risk of major depression is inversely associated with per capita fish consumption. Several other studies have demonstrated that in depressed subjects, there is a lower total omega-3 fatty acid content in the membranes of red blood cells and plasma (liquid part of the blood) when compared to control subjects. Treatment data from studies of major depressive disorder also support a role for omega-3 fatty acids, especially when omega-3 fatty acids are used as an adjunctive treatment, i.e., fatty acids are administered along with another therapeutic compound during treatment of major depressive disorder.