Depressive Disorder, Treatment-Resistant

**Definition:** Failure to respond to two or more trials of antidepressant monotherapy or failure to respond to four or more trials of different antidepressant therapies. (Campbell's Psychiatric Dictionary, 9th ed.)

**Tree numbers:** - F03.600.300.388

**Synonyms:** - Treatment Resistant Depression - Refractory Depression - Therapy-Resistant Depression