Taking in consideration the contradictory results published in the literature, and the fact that we previously reported that ABCB1 polymorphisms were associated with the risk of depression among male patients [21], in this paper we wanted to address the influence of ABCB1 polymorphisms in AD response phenotypes, in a cohort of Major Depressive Disorder (MDD) Portuguese patients. The gene discussed is ABCB1; the disease is major depressive disorder.