Objective:Electroconvulsive therapy (ECT) is regarded by many clinicians as the most effective treatment for treatment-resistant bipolar depression, but no randomized controlled trials have been conducted, to the authors’ knowledge. They compared efficacy measures of ECT and algorithm-based pharmacological treatment in treatment-resistant bipolar depression.Method:This multicenter, randomized controlled trial was carried out at seven acute-care psychiatric inpatient clinics throughout Norway and included 73 bipolar disorder patients with treatment-resistant depression. The patients were randomly assigned to receive either ECT or algorithm-based pharmacological treatment. ECT included three sessions per week for up to 6 weeks, right unilateral placement of stimulus electrodes, and brief pulse stimulation.Results:Linear mixed-effects modeling analysis revealed that ECT was significantly more effective than algorithm-based pharmacological treatment. The mean scores at the end of the 6-week treatment period were lower for the ECT group than for the pharmacological treatment group: by 6.6 points on the Montgomery-Åsberg Depression Rating Scale (SE=2.05, 95% CI=2.5–10.6), by 9.4 points on the 30-item version of the Inventory of Depressive Symptomatology–Clinician-Rated (SE=2.49, 95% CI=4.6–14.3), and by 0.7 points on the Clinical Global Impression for Bipolar Disorder (SE=0.31, 95% CI=0.13–1.36). The response rate was significantly higher in the ECT group than in the group that received algorithm-based pharmacological treatment (73.9% versus 35.0%), but the remission rate did not differ between the groups (34.8% versus 30.0%).Conclusion:Remission rates remained modest regardless of treatment choice for this challenging clinical condition.