INTRODUCTION: Pharmacological treatment of major depressive episodes in bipolar disorder (BD) is characterized by suboptimal efficacy rates, poor tolerability and adherence, delayed onset of action, and iatrogenic mood swings. The use of repetitive transcranial magnetic stimulation (rTMS) has been presented as an effective, safe and well-tolerated alternative to the treatment of uni- and bipolar depressive episodes. Recently, a new rTMS protocol was introduced, theta-burst stimulation (TBS), whose studies have shown similar efficacy with a shorter time interval than conventional rTMS. Most clinical trials performed to date evaluate the use of TBS in patients with unipolar depression or mixed samples of uni and bipolar patients. The effectiveness of TBS exclusively in BD has not been properly studied. METHODS: We will perform a 6-week, double-blind, randomized, parallel-group, sham-controlled clinical trial of active or sham TBS. We will recruit 60 patients aged between 18 and 65 years with a diagnosis of BD type I in a current moderate or severe major depressive episode resistant to at least two first- or second-line pharmacological treatments, according to CANMAT guidelines. The primary outcome measure will be the assessment of TBS efficacy through difference in scores on 17-item Hamilton Depression Scale (HAM-D) from baseline until the end of week 6 of intervention between active and sham groups. KEYWORDS: randomized clinical trial; transcranial magnetic stimulation; bipolar affective disorder; major depression.

Inclusion Criteria:

• Current moderate or severe major depressive episode in bipolar I disorder assessed with Hamilton Depression Rating Scale (HAM-D) score ≥ 17 points.
• Any appropriate first or second line pharmacological regimen in accordance with Canmat guidelines to treat a major depressive episode in bipolar I disorder:

Quetiapine 300 - 600 mg/dia; Lithium serum levels 0,6 - 1,2 meq/L; Lamotrigine 100 - 200 mg/dia; Lurasidone 20 - 120 mg/dia; Divalproex; Lithium/Divalproex + Lurasidone; Lithium/Divalproex + Lamotrigine; Olanzapine 5 - 20 mg/day + Fluoxetine 20 - 60 mg/day; Lithium/Divalproex + SSRI/Bupropion.

Exclusion Criteria:

• Concomitant diagnosis of other neuropsychiatric disorders such as: schizophrenia, dementias, mental retardation, organic mental disorder, or epilepsy;
• Acute suicide ideation (assessed by interview and clinical evaluation);
• Acute psychotic depression (assessed by interview and clinical evaluation);
• Suspected or confirmed pregnancy;
• Women in breastfeeding;
• Severe or unstable clinical disease;
• Previous rTMS treatment;
• Specific contraindications to TBS: previous epileptic seizures; change in electroencephalogram at some point in life; previous stroke; previous severe traumatic brain injury (with neurosurgery); metallic object on head (except mouth) as projectile piece, surgical clip, welding fragments; any implanted device (cardiac pacemaker, intravenous catheter).