- to at least 2 different antidepressant treatments, defined as resistance to a minimum of two antidepressant drug trials of adequate dose and duration in the current episode or previous episodes, adequacy being defined as a minimum level of three on the ATHF per antidepressant drug trial (those who have not completed antidepressant trials of adequate dose and duration due to intolerance to therapy may be included if they have demonstrated intolerance to three or more antidepressant medications in the current or a previous episode)