Depression refers to a set of prevalent, extremely debilitating disorders that can be characterized by a triad of symptoms: extreme anhedonia (complete loss of pleasure from previously pleasurable activities), depressed mood, and low energy. Other cognitive symptoms (for example, pessimistic thoughts, feelings of guilt, low self-esteem, and suicidal ideations) and somatic symptoms (for example, sleep and psychomotor disturbances, and food-intake and body-weight dysregulation) are also often present. Unipolar major depression (unipolar refers to the presence of one pole or one extreme of mood, namely depressed mood) is the leading cause of disability worldwide and is associated with a high mortality due to suicide and increases in mortality in comorbid somatic disorders such as cardiovascular disorders or cancer.