Effectiveness The severity of depression at which antidepressants show consistent benefits over placebo is poorly defined. In general, the more severe the symptoms, the greater the benefit 1,2 . Antidepressants are normally recommended as first-line treatment in patients whose depression is of at least moderate severity. Of this patient group, approximately 20% will recover with no treatment at all, 30% will respond to placebo and 50% will respond to antidepressant drug treatment 3 . This gives a NNT of 3 for antidepressant over true no-treatment control and an NNT of 5 for antidepressant over placebo. Note though that response in clinical trials is generally defined as a 50% reduction in depression rating scale scores, a somewhat arbitrary dichotomy, and that change measured using continuous scales tends to show a relatively small mean difference between active treatment and placebo.