Depression refers to a series of mental health issues characterized by loss of interest and enjoyment in everyday life, low mood and selected emotional, cognitive, physical and behavioral symptoms. Depression is a common disorder, affecting 5–15% of the general population. When diagnosed as major depressive disorder (MDD), patients are currently treated with pharmacological agents such as serotonin or noradren-aline uptake inhibitors (SSRI or SNRI) or tricyclics. Patients that fail to respond to two or more antidepressant drugs - at an adequate dose for an adequate duration given sequentially – are considered affected by treatment-resistant depression (TRD). TRD patients account for the 12–28% of the total MDD patients in charge to mental health ser-vices and are generally eligible to adjunctive pharmacotherapies with antipsychotics or lithium, behavioral therapies or electroconvulsive treatment (ECT). Unfortunately, several TRD patients display a per-sistent lack of response to the current adjunctive treatments, resulting in a relevant social burden and incurring in high direct medical costs to the health care system.