Serial IV Ketamine for Bipolar Depression: Ontario RCT Results

Serial IV Ketamine Infusions Significantly Reduce Bipolar Depression Symptoms

A double-blind, randomized controlled trial (RCT) conducted across three Ontario sites from July 2022 to November 2025 provides the strongest evidence to date that serial intravenous (IV) ketamine infusions are effective and well tolerated for treatment-resistant bipolar depression (TRBD). The Ket-BD study (ClinicalTrials.gov Identifier: NCT05004896) enrolled 68 adults with bipolar I or II disorder experiencing moderate to severe depressive episodes despite at least two failed pharmacotherapies. Participants received four infusions over two weeks of either ketamine (0.5–0.75 mg/kg) or midazolam (active placebo), adjunctive to stable mood stabilizer or antipsychotic regimens. The primary outcome—change in Montgomery-Åsberg Depression Rating Scale (MADRS) scores at day 14—showed a significant reduction in the ketamine group (mean difference −7.3 points; 95% CI, −12.0 to −2.5; P = .003; Cohen d = 0.7), indicating a moderate-to-large effect size. This direct comparison with midazolam, a psychoactive control, strengthens the finding of ketamine’s antidepressant efficacy in this challenging population.

Mechanism and Context: Ketamine’s Role in Mood Disorders

Ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, has emerged as a rapid-acting antidepressant in major depressive disorder (MDD), but its use in bipolar depression has been limited by concerns about mood destabilization. The Ontario trial is notable for its rigorous assessment of safety, with no cases of mania, hypomania, psychosis, or suicide attempts observed in either group. Only one case of subthreshold hypomanic symptoms occurred in each arm, suggesting that, under close monitoring and with mood stabilizer co-administration, ketamine does not appear to trigger manic switches in the short term. This finding addresses a key clinical and regulatory concern and distinguishes this trial from earlier, smaller studies that lacked active controls or systematic safety monitoring.

Importantly, the study required participants to maintain at least one mood stabilizer or antipsychotic, a protocol detail that may be critical for minimizing risk in bipolar populations. This approach aligns with emerging consensus in the field but is not yet universally reflected in practice guidelines, highlighting a potential decision criterion for future protocol design and clinical rollout.

Policy and Research Implications: Toward Broader Access and Guideline Updates

The robust efficacy and safety data from this RCT may influence clinical guidelines, payer coverage, and regulatory pathways for ketamine in bipolar depression. Currently, IV ketamine is approved by Health Canada and the U.S. Food and Drug Administration (FDA) only for treatment-resistant unipolar depression, with most insurers excluding bipolar indications. These new results could support off-label use or even formal label expansion, especially if replicated in larger or multi-jurisdictional studies.

• Guideline committees—such as those of the Canadian Network for Mood and Anxiety Treatments (CANMAT) and the American Psychiatric Association (APA)—may now consider updating recommendations to include ketamine as an adjunctive option for TRBD under specialist supervision.
• Payer policy could shift if cost-effectiveness analyses, using these effect sizes, demonstrate value in reducing hospitalizations or suicidality in this high-risk group.
• Regulatory agencies may require additional post-marketing surveillance or real-world evidence to address long-term safety and durability of effect, but the absence of acute mania or psychosis in this trial is a notable milestone.

One non-obvious implication is that the study’s use of midazolam as an active control, rather than saline, may have reduced expectancy effects and improved blinding, strengthening the validity of the findings. This methodological choice sets a new standard for future psychedelic and rapid-acting antidepressant trials in mood disorders.

Risks, Unknowns, and Future Directions

While IV ketamine was well tolerated over two weeks, several risks and knowledge gaps remain. The trial’s short duration precludes conclusions about long-term safety, risk of substance misuse, or sustained antidepressant effects. The exclusion of patients with recent mania or psychosis limits generalizability to broader bipolar populations. Additionally, nearly half of participants correctly guessed their treatment allocation after the first infusion, suggesting some potential for unblinding despite the active control.

Another failure mode not widely discussed is the risk of protocol drift if ketamine is adopted in less controlled outpatient settings without required mood stabilizer co-therapy or adequate monitoring for emergent mania. This could lead to adverse events that undermine both patient safety and public trust, particularly as ketamine clinics proliferate outside academic centers.

Future research should address optimal dosing schedules, maintenance strategies, and comparative effectiveness versus other emerging treatments (e.g., esketamine, neuromodulation). Long-term, multi-site registries and pragmatic trials will be essential for understanding real-world outcomes and informing regulatory and payer decisions.

Conclusion: A Step Forward, With Cautious Optimism

The Ket-BD Ontario RCT provides compelling evidence that serial IV ketamine infusions, adjunctive to mood stabilizers or antipsychotics, are effective and acutely safe for treatment-resistant bipolar depression. This may pave the way for expanded clinical use, guideline updates, and insurance coverage, but careful attention to protocol fidelity and long-term monitoring will be critical as the field moves from research to practice.

How we research: This article was written and reviewed by Dr. Alex R. Mendel, MD, MSc (psychiatry, University of Toronto), on 2026-09-04. All primary data and regulatory references are cited directly from trial registry and agency sources.