According to a study published in the Journal of Clinical Psychiatrythe largest ever conducted on the role of omega-3 fatty acids in treating major depressionfish oil supplements may improve symptoms in people diagnosed with depression who don't have an accompanying anxiety disorder.
Previous research has suggested that omega-3s, found naturally in fatty fish like mackerel and salmon, might positively affect neurotransmitter activity, which is believed to be an important factor in many mood disorders including depression. This study, done in Canada, looked at a specific type of fish oil supplement with a high concentration of eicosapentaenoic acid (EPA), which is believed to be particularly useful for depressed patients who fail to respond to antidepressants.
Participants took supplements containing 1,050 mg of EPA for eight weeks. While this research is encouraging, more studies need to be done directly comparing omega-3s with conventional antidepressants. For now, it is potentially helpful to take fish oil in addition to an antidepressant, but there is no evidence for using it alone or instead of traditional medications.