A 30-year-old male with major depressive disorder has only e…

A 30-year-old male with major depressive disorder has only experienced minimal reduction in depressive symptoms after 10 weeks of treatment with Celexa (citalopram) 40mg daily. He complains of nearly complete loss of sexual desire and difficulty attaining or maintaining an erection. The sexual dysfunction is causing problems in his marriage. He has no previous medication problems and no substance misuse. What is the best next step?