The onset of activity of antidepressants is a clinically and theoretically important criterion of efficacy. We estimated the onset of activity by an intraindividual regression analytical approach. It is assumed that efficient treatment causes a fast shift of depression scores from a baseline level to an end level. From this assumption follows a limited number of opportunities for the onset of activity to occur. These opportunities correspond to different regression models which are estimated for each patient's depression course. The day of onset is concluded from the regression model which produces the best fit to the empirical depression curve. Results of a double-blind clinical trial comparing mianserin and amitriptyline are reported (n = 28). The methodological approach confirms that observer ratings by physicists show a significantly earlier onset of activity than self ratings by the patients. The D-S also shows a significantly earlier onset of activity of mianserin compared to amitriptyline. The discussion emphasises methodological aspects.

Is the onset of efficacy of antidepressants always delayed and which early clinical signs predict final outcome of therapy ? Our analyses show that strict response criteria produce necessarily later onset estimations rather than less strict ones. In two large-scale clinical samples we compared different estimation methods of the day of onset. Patients' direct ratings produced the earliest onset estimations. Because of the strong dependency of onset estimations on measurement methods, we argue that it is still open to debate, in which degree drug response is delayed. Concerning early clinical signs of final outcome we compared early changes of the Hamilton Rating Scale for Depression (HAM-D) items with several measures of final outcome. From the data we analyzed, there are no sufficiently precise signs of final outcome within the first 2 weeks of therapy.