The main findings in the present study were: (1) SERT binding was lower in suicides independent of sex, but dependent on MDD diagnosis; higher SERT binding is associated with AUD; (2) 5-HT1A binding was greater in suicides, independent of MDD, while AUD was associated with higher 5-HT1A binding but only in suicides; (3) 5-HT2A binding was greater in suicides only when accounting for the effects of MDD and AUD in the model. Here, SLC6A4 is linked to major depressive disorder.