Of all the common mental health disorders, relapse has mostly been studied in major depressive disorder (MDD); thus, the differentiation of relapse and recurrence especially holds for MDD. Even though psychological and pharmacological treatments are effective for most mental health disorders, the return of symptomatology after a remission (or a substantial reduction of symptomatology) is common. The terms relapse and recurrence both refer to a clinically significant deterioration following a period of symptomatic improvement in MDD (response, remission, or recovery). Current consensually agreed, commonly used definitions of these change points in depression are as follows.

• Response is a construct usually used to refer to improvement, operationalized in terms of no longer meeting the diagnostic criteria for an episode of major depression and often by a proportionate ...