This cross-sectional study involved 126 male opiate-dependent patient who were tested for total testosterone (TT) and prolactin levels, and were interviewed and completed the Sexual Desire Inventory-2 (SDI-2), Malay language of International Index of Erectile Function (Mal-IIEF-15) and the Malay version of the self-rated Montgomery-Asberg Depression Rating Scale (MADRS-BM) questionnaires. The gene discussed is PRL; the disease is major depressive disorder.