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Roger S McIntyre

University of Toronto, University Health Network

138 papers in the library · 4,098 citations · publishing 0-2026

Papers

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Ketamine's mechanisms of action in major depressive disorder and treatment-resistant depression: Is brain topological change a candidate convergent systems-level pathway?

Asian Journal of Psychiatry October 12, 2026 Gia Han Le, Sabrina Wong, Simryn Selby et al.

Ketamine is a rapid-acting antidepressant with demonstrated efficacy in major depressive disorder and treatment-resistant depression, yet the mechanisms by which its molecular actions translate into sustained clinical improvement remain incompletely understood. Prevailing models have emphasized N-methyl-D-aspartate receptor antagonism and downstream glutamatergic signaling; however, convergent...

Pharmacological, clinical, and translational evidence for N,N-dimethyltryptamine, 5-methoxy-N,N-dimethyltryptamine, and zalsupindole: a systematic review.

Progress in neuro-psychopharmacology & biological psychiatry October 6, 2026 Chad Collyer, Gia Han Le, Maryam Hassan et al.

Short-acting tryptamine psychedelics are emerging as candidate psychiatric therapeutics with pharmacological profiles that may offer practical advantages over longer-acting psychedelics. N,N-dimethyltryptamine (N,N-DMT) and 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) differ in pharmacokinetic, receptor, and phenomenological properties, while zalsupindole is a putatively non-hallucinogenic...

Psilocybin for Anhedonia in Unipolar and Bipolar Depression: A Systematic Review of Clinical and Preclinical Evidence

Journal of Psychiatric Research October 1, 2026 Erica Kaczmarek, Sabrina Wong, Noah Chisamore et al.

Background Anhedonia is a debilitating core feature of mood disorders, and is associated with significant functional impairment and poor quality of life. Psilocybin has recently emerged as a novel antidepressant treatment in MDD, however, its effects on anhedonia specifically have yet to be systematically reviewed. This review evaluates available clinical and pre-clinical research, exploring...

Exploratory safety, tolerability, and feasibility of psilocybin-assisted psychotherapy for adults with co-occurring treatment-resistant depression and cluster B personality disorders

npj Mental Health Research September 16, 2026 Orly Lipsitz, Ryan M Brudner, Zoe Doyle et al.

Cluster B personality disorders (PDs) are highly comorbid with depression and are associated with attenuated antidepressant response. No clinical trials to date have reported on psilocybin-assisted psychotherapy (PAP) in comorbid treatment-resistant depression (TRD) and PDs. This is the first clinical trial to describe a subgroup of ten participants with a comorbid PD ( n = 9 cluster B; n = 1...

Cognitive effects of ketamine and esketamine treatment for major depressive and bipolar disorder: a systematic review.

Psychiatry Research September 14, 2026 Kelei Xiao, Yealin Woo, Christine E. Dri et al.

Cognitive impairment is a core feature of major depressive disorder (MDD) and bipolar disorder (BD). Most conventional antidepressants do not have direct and clinically relevant procognitive effects. Ketamine and esketamine are effective in treating treatment-resistant depression (TRD). Herein, this systematic review aims to evaluate the effects of both pharmacotherapeutics on cognitive...

The effect of ketamine on mitochondrial bioenergetics, viability, and function: A systematic review.

Journal of Psychopharmacology September 7, 2026 Sabrina Wong, Gia Han Le, Simryn Selby et al.

Extant literature indicates mitochondrial dysfunction may contribute to the pathophysiology of depressive disorders. Preclinical data indicate that anesthetic doses of ketamine are associated with deficits in mitochondrial viability and function. Ketamine and esketamine have demonstrated rapid antidepressant effects in persons with difficult-to-treat depressive disorders. Herein, we aim to...

Serial Ketamine Infusions for Treatment-Resistant Bipolar Depression

JAMA Psychiatry September 2, 2026 Diana Orsini, Sara Di Luch, George Tomlinson et al.

Importance Antidepressant efficacy of intravenous (IV) ketamine has been demonstrated in major depressive disorder; however, the efficacy and safety of ketamine for bipolar depression remain largely unknown, with limited data available in this specific population. Objective To evaluate the efficacy, safety, and tolerability of adjunctive IV ketamine compared with midazolam for...

A Systematic Review of Long-term Safety Outcomes of Ketamine and Esketamine in Patients with Treatment-resistant Depression.

August 17, 2026 Tychique T. Wasolua, Morgan S. Hardy, Tanner J. Bommersbach et al.

INTRODUCTION: Approximately 30-40% of patients with major depressive disorder fail to respond to conventional antidepressants. Ketamine and esketamine are increasingly used, yet synthesized data on cumulative safety remain limited. This systematic review evaluated long-term safety of both agents. METHODS: MEDLINE, PsycINFO, Embase, and Cochrane Library were searched from inception through...

Intranasal Ketamine for Existential Distress in Advanced Cancer.

Journal of Pain and Symptom Management August 1, 2026 Stefan Aguiar, Mary Makarious, Orly Lipsitz et al.

Depression and existential distress are highly prevalent among patients with advanced cancer, and there is growing evidence for ketamine as a rapidly acting antidepressant in the population, but few studies have examined existential distress outcomes with ketamine treatment. The INKeD-PC trial demonstrated efficacy of intranasal racemic ketamine for depression in patients with cancer receiving...

A scoping review: ketamine or esketamine when used to assist psychotherapy or in combination with psychotherapy for the management of depression in adults

npj Mental Health Research July 27, 2026 Jennifer Swainson, P. Grewal, S. Polard et al.

This scoping review maps literature for use of ketamine or esketamine with psychotherapy for depression or depressive symptoms. Forty-seven studies were identified including 4/47 (9%) randomized controlled trials, 4/47 (9%) open label trials, 27/47 (57%) observational or retrospective studies, and 12/47 (26%) individual case reports. Studies were categorized as Ketamine/Esketamine Combined with...

Ketamine Infusions and Rapid Reduction of Suicidal and Depressive Symptoms in Major Depressive Episode: A Systematic Review and Meta-Analysis.

JAMA Psychiatry July 1, 2026 Sung Ryul Shim, Hye Su Jeong, Tanner J. Bommersbach et al. 1 citation

While intravenous ketamine is not approved by the US Food and Drug Administration, it is increasingly used with off-label indications as a novel treatment for suicidal and depressive symptoms. To systematically review and metasynthesize the efficacy and safety data for intravenous ketamine in treating major depressive episodes (MDEs). PubMed, PsycInfo, Cochrane Library, and Embase were...

Evaluating the abuse liability of ketamine in the treatment of mood disorders: A systematic review.

Journal of Psychopharmacology June 24, 2026 Shreya Vasudeva, Gabrielle F. M. Lovell, Sabrina Wong et al.

Ketamine has emerged as a promising rapid-acting treatment for mood disorders and suicidality. Notwithstanding its replicated antidepressant efficacy, ketamine-associated risk for abuse, dependence, and misuse remain. We conducted a systematic review of clinical and preclinical studies from database inception to August 2025, including randomized and observational trials, open-label extensions,...

Ketamine for the Treatment of Obsessive-Compulsive Disorder (OCD): A Systematic Review on Efficacy and Tolerability.

Clinical Neuropharmacology June 19, 2026 Isabela Heroiu, Gia Han Le, Maria‐christina Sioufi et al.

This systematic review aims to assess the efficacy and tolerability of ketamine in the treatment of obsessive-compulsive disorder. Obsessive-compulsive disorder is a chronic and severe disorder characterized by intrusive thoughts and repetitive behaviours that can cause significant distress. Notwithstanding current treatments and interventions for obsessive-compulsive disorder, some individuals...

The effect of glutamatergic modulators on sleep behavior and architecture in depressive disorders: A systematic review.

Journal of Psychiatric Research June 1, 2026 Kyle Valentino, Hana Ballum, William Cheung et al.

Approximately 80% of individuals diagnosed with major depressive disorder (MDD) report symptoms of insomnia. Glutamatergic modulators, such as ketamine, are reported to be effective for the treatment of depressive symptomatology in adults with MDD. Disrupted glutamate homeostasis is linked to poor sleep quality and sleep disorders. Herein, we sought to systematically determine the effect of...

DOI: 10.1016/j.jpsychires.2026.02.011 (opens in new tab) Full text (opens in new tab) Depression Early morning awakening Gamma-aminobutyric acid gaba Glutamate +2

The Serotonin 2B (5‐ HT2B ) Receptor: A Narrative Review of Preclinical and Clinical Evidence on the Safety Considerations and Therapeutic Potential for the Treatment of Depression

Clinical Pharmacology & Therapeutics May 28, 2026 Gia Han Le, Sabrina Wong, Danica E. Johnson et al.

Major depressive disorder (MDD) and treatment-resistant depression (TRD) remain leading causes of disability, providing the impetus for receptor-level treatment strategies beyond monoamine reuptake. The serotonin 5-HT2B receptor (5-HT2BR) is uniquely positioned at the interface of central-antidepressant mechanisms and peripheral cardiac risks. Herein, we reviewed preclinical, translational and...

Structural Neurotoxic and Neuroprotective Effects of Ketamine and Esketamine in Preclinical and Human Studies: A Systematic Review

Research Square May 27, 2026 Tychique T. Wasolua, Tanner J. Bommersbach, Roger S McIntyre et al. preprint

Abstract Ketamine and esketamine are increasingly used as rapid-acting antidepressants, yet concerns remain regarding potential structural neurotoxicity, particularly with chronic or high-dose exposure. Despite expanding clinical use, no comprehensive systematic review has integrated neurotoxicity evidence across preclinical and human studies while formally evaluating methodological quality....

A systematic review of ketamine and esketamine-induced long-term potentiation and synaptic scaling: Do the molecular and synaptic plasticity effects inform dosing intervals?

Journal of Affective Disorders April 15, 2026 Gia Han Le, Sabrina Wong, Danica E. Johnson et al. 4 citations

Ketamine and esketamine exhibit rapid antidepressant effects in persons with treatment-resistant depression (TRD) and bipolar depression (TRBD). However, the synaptic mechanisms governing dose, frequency, and durability of response remain unclear. This review aims to evaluate the dosing parameters, including minimum dose and optimal dosing intervals, that reliably induce or maintain long-term...

Blinding Integrity in Psychedelic Randomized Clinical Trials

JAMA Psychiatry April 15, 2026 Diana Orsini, Sabrina Wong, Sara Di Luch et al. 4 citations

Importance: Psychedelic drugs possess acute psychoactive effects that can compromise blinding integrity in randomized clinical trials (RCTs). Functional unblinding, when participants or raters correctly identify treatment allocation based on subjective effects, may bias outcomes through expectancy effects, challenging the validity of efficacy estimates and regulatory acceptance. Objective: To...

DOI: 10.1001/jamapsychiatry.2026.0255 (opens in new tab) Blinding Randomized controlled trial Clinical trial Meta-analysis +4

The effect of dextromethorphan on reward-related behaviors: A systematic review of preclinical and clinical evidence.

Journal of Affective Disorders April 1, 2026 Kayla M Teopiz, Gia Han Le, Sabrina Wong et al.

Extant literature suggests that anhedonia, defined as a loss of the ability to feel pleasure or interest, is subserved by dysregulation of reward processing in the central nervous system. Dextromethorphan (DXM), an uncompetitive N-Methyl-d-Aspartate (NMDA) receptor antagonist and sigma-1 (σ1) receptor agonist, is a glutamatergic modulator with antidepressant properties. The effect of DXM on...

Effect of Ketamine on Reward Processing in Depressive Disorders: A Systematic Review of Neuroimaging Studies

CNS Spectrums March 10, 2026 Halima Faisal, Gia Han Le, Angela T H Kwan et al.

Background: Anhedonia and reward-processing deficits are core features of major depressive disorder (MDD) that respond poorly to traditional antidepressants.Ketamine has rapid antidepressant effects, yet its neurofunctional actions within reward circuits remain unclear.We synthesized human neuroimaging evidence on ketamine-related modulation of reward circuitry and implications for...

The use of repetitive transcranial magnetic stimulation (rTMS), electroconvulsive therapy (ECT), ketamine, and esketamine in reducing suicidality in major depressive disorder: A comprehensive narrative review

Psychiatry Research February 19, 2026 Trisha Menon, Andy Lu, Akhilan Arulmozhi et al.

Ketamine, esketamine, rTMS and ECT are associated with reductions in SI in persons with MDD, with the strongest evidence from randomized controlled trials supporting rapid, short-term effects, particularly for ketamine and esketamine. Further characterization and differentiation of the durability of antisuicidal effects of the aforementioned interventions requires investigation in large-scale,...

Examining the effects of psilocybin-assisted psychotherapy on anhedonia in treatment-resistant depression

Journal of Affective Disorders February 12, 2026 Erica Kaczmarek, Nelson Rodriguez, Noah Chisamore et al.

Anhedonia, a core symptom of depression, is often resistant to conventional treatments and significantly impacts quality of life. This secondary analysis aimed to evaluate the effects of psilocybin-assisted psychotherapy (PAP) on anhedonia severity in individuals with treatment-resistant depression (TRD). Participants (n = 30) with TRD and a primary diagnosis of Major Depressive Disorder or...