Depression is one of the current dilemmas in both developed and developing societies. Studies show that the severity of psychiatric symptoms is directly related to the degree of inflammation caused by cytokines secreted by the immune system. Hence, evaluating serum cytokine levels in patients with depression can help to understand the pathogenesis of the disease and make the best therapeutic decisions. The present study investigated the levels of inflammatory cytokines, tumor necrosis factor-α (TNF-α), interleukin-1 (IL-1), and interleukin-6 (IL-6) in patients with major depression or bipolar disorder during depressive episodes (BDDE) before and after a 6-month pharmaceutical intervention. Patients referring to 3 clinics were recruited for the study. The diagnosis of major depression or bipolar disorder in a depressive phase was made according to the Diagnostic and Statistical Manual of Mental Disorders -5(DSM-5) criteria. There was a significant difference in depression levels between the pre-intervention and 6-month follow-up in both groups. After 6 months, IL-1 and IL-6 levels in the bipolar disorder group had decreased while TNF-α levels had increased. There was also a significant difference between pre-intervention and follow-up levels of IL-1.  Serum levels of IL-1 and IL-6 decreased significantly in both groups after the 6-month follow-up, and symptom improvement was observed. TNF-α levels, on the other hand, decreased in the major depression group but increased in the bipolar disorder group. Considering that inflammation is a major outcome of depression, treatment strategies to reduce inflammation could be a practical approach to improving psychiatric symptoms.