Pattern analysis has been used to distinguish between the true effect of an antidepressant and a placebo effect. The placebo effect constitutes clinical improvement that is attributable to the caregiver, treatment setting, or placebo substance. Pattern analysis allows identification of patients who have early persistent responses, delayed persistent responses, or no responses to a drug. In our study, we used this method to assess the onset and persistence of antidepressant activity of high daily doses of venlafaxine. Our analysis considered scores on the Global Improvement item of the Clinical Global Impressions scale for intent-to-treat patients in two double-masked, placebo-controlled studies of at least 6 weeks' duration. Dosages in both studies were rapidly titrated upward so patients received at least 200 mg/d within the first week of treatment. Improvement within the first 2 weeks was considered early, and improvement not followed by a relapse through the scheduled end of treatment was considered persistent. Significantly greater percentages of patients in the venlafaxine group (27% and 20% in study 1 and study 2, respectively) than in the placebo group (9% and 2.%, respectively) had a clinically meaningful drug response within the first 2 weeks of treatment. This early response persisted for the duration of each trial. We concluded that venlafaxine in dosages of at least 200 mg/d demonstrates an early and persistent onset of efficacy compared with placebo.
