Major depressive disorder (MDD) is a prevalent mental illness associated with significant impairment in quality of life and treatment resistance in as many as 50% of patients. Few alternatives to psychopharmacological and electroconvulsive therapy (ECT) exist. Transcranial magnetic stimulation (TMS) is one such alternative with demonstrated efficacy in the treatment of both MDD and treatment- resistant depression (TRD). Accrued evidence from meta-analyses suggests that rTMS has moderate effect sizes in both MDD and TRD, comparable, though less robust, to those seen in ECT treated patients, and similar to those seen with antidepressant treatment in TRD. To date, rTMS has been used in adult, pediatric, and geriatric populations with success. Predictors of response include lower age, lower degrees of treatment resistance, and the absence of comorbid anxiety or psychotic symptoms. rTMS is cost-effective when compared to existing treatments for TRD including psychopharmacological interventions and ECT. More research, however, is needed to determine the most optimal stimulation parameters. Accelerated treatment over a short duration of time, sequential bilateral stimulation, extended number of pulses per session are potential methods of optimizing efficacy over current unilateral stimulation protocols. The extent to which rTMS can be pushed to engender the greatest possible clinical effects while avoiding seizure induction remains unknown.

Transcranial magnetic stimulation, treatment resistant depression, brain stimulation, cost-effectiveness, Major depressive disorder (MDD), electroconvulsive therapy (ECT), comorbid anxiety, psychotic symptoms, clinical effects, seizure induction

Centre for Addiction and Mental Health, Department of Psychiatry, University of Toronto, Toronto, Ontario, Canada.