This is a randomized, double-blind clinical trial to evaluate the efficacy of Atorvastatin in treating major depressive disorder. In this study 60 patients, referred to psychiatry ward of Farshchian Hospital will be enrolled in the study with consent inform ,who have been diagnosed as MDD based on DSM-IV TR and their age is between 18 to 50 years and have no known systemic disease and hypercholesterolemia and also have no history of illegal substance abuse. The patients will be divided into two groups based on randomized blocks. The case group will receive 40 mg citalopram along with atorvastatin 20 mg per day and the control group will receive 40 mg citalopram along with placebo. Prior to start the treatment, they will undergo ALT, AST, LDH, CPK, LDL, HDL, CHOL, and TG tests. Before the treatment and the intervals of 3, 6 and 12 weeks after the treatment, the patients’ depression wiil be assessed through Hamilton Depression Scale and finally the improvement rate of the both groups compared to each other.