Are 2-week trials sufficient to indicate efficacy?

The belief in delayed antidepressant action has been encouraged by a confusion between the concepts of full response and the appearance of improvement. Conventional trial designs are insufficiently sensitive to detect early significant separation of drug and placebo. Analysis of time to response is a more sensitive measure to detect early differences in improvement and 2-week studies are therefore proposed as a valid method to demonstrate antidepressant efficacy.