DURATION OF ANTIDEPRESSANT TRIALS - CLINICAL AND RESEARCH IMPLICATIONS

The objective of our study was to demonstrate that additional antidepr essant benefit occurs between weeks 4 and 6 in adult outpatients, even when dose is not increased. Response between weeks 4 and 6 was studie d among depressed outpatients randomly assigned to imipramine, phenelz ine, or placebo under double-blind conditions. Patients were selected for analysis only if they did not have a dose increase after the start of the fourth week of treatment (day 22). Eighty-eight patients met t his condition. Conditional probability analysis was performed. Nonresp onders to 4 weeks (28 days) of treatment had a significantly greater L ikelihood of responding by week 6 if they were on phenelzine rather th an placebo. The same is probably true for patients on imipramine. In r esearch and clinical care, 4 weeks is too short a trial of phenelzine to conclude a lack of efficacy. Four weeks is probably also too short a trial of imipramine.