In a study of major depression, 423 adults who reported depressive episodes lasting at least four weeks took 1,050 mg of EPA plus 150 mg of DHA (docosahexaenoic acid) per day or a placebo. About 40 percent were also taking anti-depressants.
After eight weeks, compared to placebo, those who took omega-3s tended to have fewer depressive symptoms. In a subgroup whose symptoms did not include anxiety, omega-3s reduced depressive symptoms as effectively as anti-depressants.