A pharmaceutical preparation comprising EPA in an appropriately assimilable form where of all the fatty acids present in the preparation at least 90%, and preferably at least 95%, is in the form of EPA and where less than 5%, and preferably less than 3%, is in the form of DHA is provided for the treatment of a psychiatric or central nervous disorder. The preparation may be administered with conventional drugs to treat psychiatric or central nervous disorders to improve their efficacy or reduce their side effects.