Mechanisms of antidepressant action: Is onset early or late?

Earlier studies of the 'onset' of antidepressant action might not have distinguished between the time when improvement first appears from when a substantial response occurs. The application of more refined statistical approaches, together with better assessments of improvement in the behavioral components of the illness, allows onset to be established in absolute terms. Recent studies, using such methodology, consistently reveal that onset of improvement occurs in two weeks or less in ultimate treatment responders.