ECT can be an effective treatment for certain patients. There is evidence that ECT is an effective treatment for depression as a single disorder [647]; however, no research studies to date have assessed the efficacy of ECT in treating co-occurring depression and AOD use disorders. The Royal Australian and New Zealand College of Psychiatrists clinical practice guidelines for the treatment of depression note that ECT is a highly efficacious treatment with a strong evidence base, particularly for severe depressive disorders [648, 649].The UK NICE Guidelines similarly recommend that ECT be considered for treating severe depressive disorders, or after other treatment options have been exhausted [650].