Major depressive disorder (MDD) is a common psychiatric disorder with a lifetime prevalence of 10–15% in most large studies. Despite the availability of medication and psychotherapeutic treatments, recurrent or chronic course is common (60–80%)1, often with comorbid anxiety or substance use disorders, substantial impact on family and work life and on physical health, and an approximately 4% risk of eventual suicide (higher in more severe cases).2 MDD is diagnosed when an individual experiences one or more major depressive episodes in the absence of other diagnoses such as bipolar-I or -II disorder, schizoaffective disorder or schizophrenia. An episode is defined as two or more weeks during which the person experiences impaired functioning and five or more key symptoms (dysphoric mood, loss of enjoyment, suicidal thoughts or acts, agitated or slowed movements, guilty or self-denigrating feelings, fatigue, and disturbances of sleep, appetite, concentration).3
