Long-term treatment of depression encompasses two separate phases: relapse and recurrence prevention. Relapse prevention aims to consolidate the response to acute treatment. Some tricyclic antidepressants (TCAs) have been shown to be effective, possibly in lower than standard acute treatment doses. The selective serotonin reuptake inhibitors (SSRIs) have been shown to be effective at the same minimum effective doses used to treat acute depression, or in a lower dose as with citalopram. Recurrence prevention aims to reduce the risk of onset of a new episode of depression in patients with recurrent depression. Imipramine has been thoroughly studied in unipolar depressed patients in full therapeutic doses for up to five years and is clearly effective. Other TCAs have not been adequately tested and may not all be equally effective. The SSRIs fluoxetine, paroxetine and sertraline have also been shown to be effective in reducing the risk of new episodes of depression.
