A single center, open label study assessing the feasibility, safety and therapeutic effect of Minocycline in adult patients with diagnosis of unipolar depression. Up to 30 patients diagnosed with unipolar depression that are in a current depressive episode. The patients will be of all racial, ethnic and gender categories, ranging from 18 to 68 years of age, and have HDRS-21≥20. All subjects will continue to take their treatment with antidepressant medications for the duration of the study. All subjects are prescribed minocycline 200 mg/day orally (2X100 mg) for the first 3 days. than, all subjects are prescribed minocycline 400 mg/day orally (2X200 mg) from day 4 until termination visit (day 35). The primary objective of this study is to assess the therapeutic effect of Minocycline in unipolar depression.