Since the optimum level of folic acid is required for normal functioning of the brain and body, this study aimed to determine the effects of adding folic acid to the diet (citalopram) was conducted in response to the treatment of patients with depression. This study is a double-blind clinical trial. The study population included all patients with depression referred to Farabi Hospital in 2014. Patients in the study and control groups were examined. In the experimental group the therapeutic dose of citalopram with folic acid were administered, but citalopram and placebo in the control group. Beck questionnaire was used to evaluate the response to treatment. The results showed that the response to treatment levels was statistically significant in the sense that the response to treatment in the study group was faster, but the two groups did not achieve statistically significant results. To determine the effect of folic acid in response to treatment of patients with depression and the need for adding it to the usual anti-depression drugs requires further studies with longer durations.