This trial aims to assess the efficacy and tolerability of Magnetic Seizure Therapy (MST) as an alternative to electroconvulsive therapy (ECT) for Bipolar Disorder (BD). Research indicates that the prevalence of treatment resistance in bipolar depression is twice that of unipolar depression. The limited effectiveness of current treatments for bipolar depression coupled with the medical and economic burden associated with the disorder engenders a need for novel therapeutic interventions that can provide greater response and remission rates.

The study will involve a randomized, double blind, non-inferiority clinical trial with two treatment arms conducted in three academic institutions (the Centre for Addiction and Mental Health (CAMH) in Toronto, Ontario; the Ontario Shores Centre for Mental Health Sciences in Whitby, Ontario; and University of British Columbia (UBC) Hospital in Vancouver, British Columbia). The investigators are pursuing a non-inferiority clinical trial in an effort to compare MST to right unilateral ultrabrief pulse ECT (RUL-UB-ECT). Treatment will be administered two to three days per week. Depression symptoms will be assessed with the 24-item Hamilton Depression Rating Scale (HRSD-24) and suicidality will be assessed with the Scale for Suicidal Ideation (SSI). Remission will be defined as HRSD-24 < or = 10 and a > 60% decrease in scores from baseline on two consecutive ratings. Once a participant reaches remission, a second rating to confirm remission will be conducted immediately before their next scheduled treatment. If remission is confirmed, they will then be considered a completer of the acute treatment course. Remission of suicidal ideation is defined as a score of 0 on the SSI. Therefore, there will be no specific minimum number of treatments that patients must receive to be classified as remitters. However, patients who do not meet remission criteria after 21 treatment sessions will be considered non-remitters and will cease treatment sessions. This maximum treatment number was chosen allowing for the possibility that MST may require more treatment sessions to achieve remission, similar to RUL-UB ECT. The blind will not be broken to participants until the completion of the entire study.

Inclusion Criteria:

Patients will be included if they:

1. are inpatients or outpatients;
2. are voluntary and competent to consent to treatment and research procedures according to ECT/MST attending psychiatrist;
3. have a MINI International Neuropsychiatric Interview diagnosis, Version 6 (MINI-6.0) diagnosis of non-psychotic Bipolar Disorder (Type I or II)
4. are 18 years of age or older
5. have a baseline HRSD-24 score > 21;
6. are considered to be appropriate to receive convulsive therapy as assessed by an ECT attending psychiatrist and a consultant anaesthesiologist
7. are agreeable to keeping their current antidepressant treatment constant during the intervention;
8. are likely able to adhere to the intervention schedule;
9. meet the MST safety criteria;
10. If a woman of child-bearing potential: is willing to provide a negative pregnancy test and agrees not to become pregnant during trial participation.

Exclusion Criteria:

Patients will be excluded if they:

1. have a history of MINI diagnosis of substance dependence or abuse within the past three months;

2. have a concomitant major unstable medical illness;

3. are pregnant or intend to get pregnant during the study;

4. have a MINI diagnosis of any primary psychotic disorder

5. have a MINI diagnosis of obsessive compulsive disorder, or post-traumatic stress disorder deemed to be primary and causing more functional impairment than the depressive disorder

6. have probable dementia based on study investigator assessment;

7. have any significant neurological disorder or condition likely to be associated with increased intracranial pressure or a space occupying brain lesion, e.g., cerebral aneurysm;

8. present with a medical condition, a medication, or a laboratory abnormality that could cause a major depressive episode or significant cognitive impairment in the opinion of the investigator (e.g., hypothyroidism with low TSH, rheumatoid arthritis requiring high dose prednisone, or Cushing's disease);

9. have an intracranial implant (e.g., aneurysm clips, shunts, stimulators, cochlear implants, or electrodes) or any other metal object within or near the head, excluding the mouth, that cannot be safely removed;

10. require a benzodiazepine with a dose greater than lorazepam 2 mg/day (or equivalent benzodiazepine) or any anticonvulsant due to the potential of these medications to limit the efficacy of both MST and ECT;

11. are unable to communicate in English fluently enough to complete the neuropsychological tests;

12. have a non-correctable clinically significant sensory impairment (i.e., cannot hear or see well enough to complete the neuropsychological tests).

    These eligibility criteria are congruent with the criteria that have been used in the major ECT trials conducted during the past decade;

13. elevated mood, defined as a score of 20 or higher on the Young Mania Rating Scale (YMRS).

Participants will be randomized into the study using a permuted block method with a random number generator. The study statistician will prepare the randomization scheme. The block size will be fixed and study personnel will be blinded to the randomization block size