Objective : To assess the variation of relative efficacy and tolerability of an antidepressant versus others based on both pre-marketing (registration studies) and post-marketing studies versus pre-marketing studies only in patients with major depressive disorder. Methods : The relative efficacy and tolerability of antidepressants was assessed by mixed treatment comparisons (MTCs) using data acquired over two time periods: before registration of the reference drug escitalopram (1989–2002) and up to 5 years later (1989–2007). Ranking probability outputs were presented for efficacy, using change from baseline to 8 weeks on Montgomery–Åsberg Depression Rating Scale total score, and tolerability, using withdrawals due to adverse events. Results : The relative efficacy and tolerability of some selected antidepressants, including escitalopram, varied considerably over the two time periods. The improved relative efficacy and tolerability of escitalopram over time, compared with citalopram, was demonstrated by greater separation of ranking probability curves for efficacy and tolerability. In 2002, escitalopram ranked low with 13.9% and 5.1% probability of being in the top four antidepressants’ relative efficacy and tolerability, respectively. In 2007, ranking probabilities for relative efficacy and tolerability of escitalopram increased to 52.5% and 82.1%, respectively. Conclusions : Time of marketing authorization may not be the most appropriate time to evaluate the relative efficacy and tolerability of a new antidepressant based on MTC approach due to the asymmetry of information between new and older compounds. However, the first evaluation of relative effect of a new drug for health technology assessment recommendations is commonly done at this time. Re-evaluation of a drug several years after its launch is likely to provide a more accurate indication of its relative efficacy and tolerability.