Major depressive disorder

According to the most recent version of the Diagnostic and Statistical Manual of Mental Disorders-5 (DSM-5) (American Psychiatric Association, 2013), major depressive disorder (MDD) is characterized by two primary diagnostic criteria: depressed mood and loss of interest or pleasure in activities (anhedonia), at least one of which must occur for at least two weeks. Secondary symptoms include significant weight loss or gain or decrease in appetite, insomnia or hypersomnia, psychomotor agitation or retardation, fatigue or energy loss, feelings of worthlessness or excessive or inappropriate guilt, attentional or concentration difficulties, and recurrent thoughts of death and/or suicide. In adults, of these symptoms, depressed mood, anhedonia, and feelings of worthlessness or guilt are most common, while weight loss, weight gain, hypersomnia, and psychomotor changes are less common (Rice et al., 2019). Globally, MDD is consistently among the most prevalent mental disorders (Vos et al., 2016; 2017) and there are 322 million people living with depressive disorders worldwide (World Health Organization, 2017). A functional analytic approach is useful for conceptualizing the disorder and its treatment. There is now considerable evidence for interventions such as behavioral activation, ACT, Problem-solving Therapy and an accumulating evidence base for interventions such as Functional Analytic Psychotherapy, Mindfulness-Based Cognitive Therapy, and Cognitive-Behavioral Analysis System of Psychotherapy.