To evaluate the effectiveness of zinc sulfate in improving depression symptoms in patients treated with selective serotonin Reuptake inhibitors in Ahvaz Golestan Hospital. A clinical demographic questionnaire will be conduct based on information obtained from the patients and their records which include items on age, education, marital status, sex, presence of other diseases such as hypertension, high cholesterol, diabetes, chronic liver failure, and kidney and lung disease. Beck Depression Inventory (BDI) will perform at baseline to measure patients’ depression. Patients with a score of 13 and higher and those who are treated with SSRI drugs for at least 3 months will be enrolled. The patients will be divided randomly into two groups of 30. One group will receive selective serotonin inhibitors (20-60 mg of citalopram or 50-200 mg of sertraline) plus zinc sulfate (25 mg daily), while the other group will receive selective inhibitors (20-60 mg of citalopram or 50-200 mg of sertraline) with placebo (25 mg of malt dextrose daily). Patients will be tested at weeks 2, 4, 6 and 8 to estimate the depression and functional level, using the BDI.