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Ketamine research: what the evidence shows

A dissociative anesthetic with rapid-acting antidepressant effects, now an approved treatment for treatment-resistant depression.

State of the evidence

Synthesized

Synthesized from 25 studies in the library · AI-generated, grounded in the abstracts below

Found by searching the library for Ketamine, racemic ketamine, arketamine, R-ketamine, then ranked by relevance.

Ketamine has the strongest, most consistent evidence as a rapid-acting antidepressant in treatment-resistant depression: a single IV infusion beat active placebo at 24 hours (about 8 points on MADRS, 64% vs 28% response), and esketamine nasal spray added to an oral antidepressant outperformed antidepressant alone and roughly halved relapse risk when continued. It also rapidly reduces suicidal ideation for up to a week, though one trial in acutely suicidal patients found mood benefit at 4-24 hours that was lost by day 25 and no reduction in clinician-rated suicide risk. Main caveats are short follow-up, dissociative and cognitive side effects, and reliance on animal work for mechanism.

Evidence by study

Direction is which way each study's own result points, not our rating of the study.

What the directions mean
Supports:
the study found the intervention worked, or its hypothesis held.
Opposes:
it found the opposite, no benefit or a harm.
No effect:
no significant difference either way.
Mixed:
effects in both directions within the same study.
Unclear:
the abstract does not report a direction.
Study Design Sample size Direction Finding
Subanesthetic Effects of the Noncompetitive NMDA Antagonist, Ketamine, in Humans 1994 RCT 19 Mixed Subanesthetic ketamine produced schizophrenia-like positive and negative symptoms, dissociative experiences, and cognitive deficits, supporting its use as a pharmacological model of psychosis and dissociation.
mTOR-Dependent Synapse Formation Underlies the Rapid Antidepressant Effects of NMDA Antagonists 2010 preclinical observational Supports Ketamine rapidly activated mTOR signaling and increased synaptic proteins and spine synapses in prefrontal cortex, and blocking mTOR abolished both the synaptogenic and behavioral antidepressant effects.
Activation of Glutamatergic Neurotransmission by Ketamine: A Novel Step in the Pathway from NMDA Receptor Blockade to Dopaminergic and Cognitive Disruptions Associated with the Prefrontal Cortex 1997 dose-response preclinical study Mixed Low-dose ketamine increased prefrontal glutamate and dopamine release via non-NMDA receptors and impaired a prefrontal cognitive task, effects ameliorated by an AMPA/kainate antagonist.
NMDAR inhibition-independent antidepressant actions of ketamine metabolites 2016 preclinical study Supports Ketamine's antidepressant effects required its metabolism to hydroxynorketamine, and the (2R,6R)-HNK metabolite produced antidepressant-related behavioral and cellular effects independent of NMDAR inhibition while lacking ketamine-related side effects.
The dissociative anaesthetics, ketamine and phencyclidine, selectively reduce excitation of central mammalian neurones by N‐methyl‐aspartate 1983 experimental study Supports Ketamine selectively blocked N-methyl-aspartate-evoked excitation of spinal neurons while sparing quisqualate and kainate responses, suggesting NMA receptor blockade contributes to its anesthetic and analgesic properties.
Ketamine and Ketamine Metabolite Pharmacology: Insights into Therapeutic Mechanisms 2018 review Supports Reviews evidence that ketamine has anesthetic, analgesic, anti-inflammatory, and antidepressant actions, that its effects involve targets beyond NMDA receptors, and that hydroxynorketamine metabolites show antidepressant efficacy preclinically.
Antidepressant Efficacy of Ketamine in Treatment-Resistant Major Depression: A Two-Site Randomized Controlled Trial 2013 RCT 73 Supports A single ketamine infusion produced greater MADRS improvement than active placebo midazolam at 24 hours (7.95-point difference) with response rates of 64% versus 28%.
Mechanisms of Ketamine Action as an Antidepressant 2018 review Supports Reviews mechanistic hypotheses for ketamine's antidepressant action, converging on strengthening of excitatory synapses via NMDAR inhibition, AMPA activation, and downstream plasticity pathways, while noting abuse potential and dissociative effects limit use.
Efficacy and Safety of Flexibly Dosed Esketamine Nasal Spray Combined With a Newly Initiated Oral Antidepressant in Treatment-Resistant Depression: A Randomized Double-Blind Active-Controlled Study 2019 phase 3 RCT 227 Supports Esketamine nasal spray plus a newly initiated oral antidepressant reduced MADRS more than antidepressant plus placebo at day 28 (4.0-point difference).
Efficacy of Esketamine Nasal Spray Plus Oral Antidepressant Treatment for Relapse Prevention in Patients With Treatment-Resistant Depression 2019 phase 3 randomized withdrawal RCT 297 Supports Continuing esketamine plus an oral antidepressant reduced relapse risk by 51% in stable remitters and 70% in stable responders compared with switching to placebo nasal spray.
Efficacy and Safety of Intranasal Esketamine Adjunctive to Oral Antidepressant Therapy in Treatment-Resistant Depression 2017 phase 2 RCT 67 Supports Intranasal esketamine produced a rapid, dose-related antidepressant effect, with response appearing to persist beyond 2 months at reduced dosing frequency.
Synthesizing the Evidence for Ketamine and Esketamine in Treatment-Resistant Depression: An International Expert Opinion on the Available Evidence and Implementation 2021 review / expert consensus Supports Concludes ketamine and esketamine are effective rapid-onset treatments for treatment-resistant depression, while flagging unresolved questions on safety, tolerability, and clinical implementation.
Ketamine Pharmacology: An Update (Pharmacodynamics and Molecular Aspects, Recent Findings) 2013 review Mixed Describes ketamine as a safe anesthetic with analgesic and antidepressant effects acting mainly through NMDA antagonism, without neurotoxicity in usual practice, but notes cognitive disturbances and frontal white matter abnormalities in chronic users and unknown consequences of repeated high doses.
The effect of a single dose of intravenous ketamine on suicidal ideation: a systematic review and individual participant data meta-analysis 2017 systematic review and individual participant data meta-analysis 167 Supports A single ketamine dose rapidly reduced suicidal ideation on clinician- and self-rated measures within one day, with moderate-to-large effect sizes persisting up to one week and partly independent of mood improvement.
Efficacy and Safety of Intranasal Esketamine for the Rapid Reduction of Symptoms of Depression and Suicidality in Patients at Imminent Risk for Suicide: Results of a Double-Blind, Randomized, Placebo-Controlled Study 2018 RCT 68 Mixed Intranasal esketamine plus standard care improved depressive symptoms more than placebo at 4 and 24 hours but not at day 25, and did not significantly reduce clinician-rated suicide risk.
Integrating multi-receptor and neuron–glia mechanisms of ketamine's antidepressant action: a convergence framework for understanding efficacy 2026 review Unclear Argues that ketamine's antidepressant efficacy likely arises from convergent multi-receptor and neuron-glia actions, that opioid effects are insufficient to explain its broader antidepressant action, and that many model components remain hypothetical.
Chronic High‐Dose Ketamine Fails to Induce a Cystitis‐Like Phenotype in Mice Despite High Urinary Metabolite Levels 2026 controlled animal experiment 40 No effect Twelve weeks of high-dose ketamine produced high urinary and plasma drug and metabolite levels but no differences from saline in voiding behavior, suprapubic sensitivity, wellbeing, or bladder and kidney histopathology.
Neural correlates of ketamine-induced dilation of temporal expectation 2026 observational animal study 2 Supports Subanesthetic ketamine dose-dependently dilated time estimation and flattened and rotated parietal delay-period population activity away from the pre-drug state.
Quality of Life in Patients with Treatment-Resistant Depression Treated with Intranasal Esketamine as Add-On Therapy to an SSRI—A Prospective, Comparative Study in Real-World Clinical Practice 2026 prospective observational cohort 60 Mixed Both groups improved in quality of life and depression severity, with larger absolute changes in the esketamine add-on group on some quality-of-life domains, though the authors caution the unassigned design precludes causal attribution.
Subanesthetic ketamine modulates region-specific neural and endocrine responses to acute stress in rats. 2026 controlled animal experiment Supports Subanesthetic ketamine reduced immobility and blunted stress-induced corticosterone rises, with region- and context-dependent changes in neuronal activation including suppressed amygdala hyperactivation.
Depression: Ketamine quiets an unruly habenula. 2026 commentary Supports Describes evidence that the ~24-hour window of ketamine's antidepressant effects coincides with reduced habenula activation and reduced aversive learning in healthy subjects.
Feeling safe: an empirical-ethical analysis of vulnerability in (es)ketamine treatment 2026 qualitative study 24 Mixed Patients emphasized therapeutic presence, physical grounding, and transitional support for feeling safe, while clinicians more often framed ketamine as a catalyst of transformation than patients did, suggesting misalignment about preparation and integration.
Ketamine administration reduced conditioned defensive behaviour and upregulated protein expression associated with neuroplasticity in a planarian model of aversive memory reactivation. 2026 preclinical experimental study 15 Supports 10 μM ketamine reduced conditioned defensive behaviors during aversive memory reactivation and was associated with enrichment of neuroplasticity-related protein pathways.
Real-world clinical outcomes under intravenous and subcutaneous esketamine protocols for treatment-resistant depression: a multicenter, retrospective study 2026 retrospective chart review 72 No effect Response rates after six sessions favored IV over subcutaneous esketamine but did not reach significance, endpoint response did not differ, and dissociation was more frequent with IV (53.8% vs 13.0%).
Esketamine alleviates the pain-depression dyad: insights from exploratory transcriptomic profiling and Wnt4-associated molecular alterations within the anterior cingulate cortex 2026 experimental animal study Supports A single 15 mg/kg esketamine dose alleviated pain hypersensitivity, behavioral despair, and anhedonia, with associated Wnt4-related and GSK3β-mTOR signaling changes and reduced synaptic markers in anterior cingulate cortex.

Points of agreement

  • Multiple RCTs and meta-analytic data show ketamine and esketamine produce rapid antidepressant effects in treatment-resistant depression, superior to active or placebo comparators at 24 hours to 28 days.
  • Continued esketamine plus oral antidepressant reduces relapse compared with discontinuation, indicating maintenance benefit beyond acute response.
  • Ketamine rapidly reduces suicidal ideation for up to about a week, with effects partly independent of overall mood change.
  • NMDA receptor antagonism is the canonical mechanism, but AMPA activation, mTOR-dependent synaptogenesis, and hydroxynorketamine metabolites are consistently implicated across preclinical and review work.
  • Dissociative, psychotomimetic, and cognitive effects are consistently reported and are a recognized limitation on broad clinical use.

Conflicts

  • One trial in acutely suicidal patients found antidepressant benefit at 4-24 hours that was no longer significant by day 25 and no reduction in clinician-rated suicide risk, whereas pooled individual-participant data found significant reductions in suicidal ideation up to one week.
  • Preclinical work attributes antidepressant action to NMDAR-independent hydroxynorketamine mechanisms, while other reviews retain NMDAR inhibition as central; the relative contribution remains contested.
  • Real-world observational data suggest larger quality-of-life gains with esketamine add-on, but the authors themselves caution this cannot be read as a causal effect, contrasting with the randomized evidence.
  • A mouse study failed to reproduce ketamine-induced cystitis despite high drug exposure, conflicting with the human literature on chronic ketamine misuse.

Gaps

  • Durability beyond a few weeks to months is largely unestablished; most controlled efficacy data stop at 28 days or shorter.
  • Blinding integrity is questionable given ketamine's distinctive dissociative effects, which may inflate active-placebo comparisons.
  • Long-term safety of repeated dosing, including cognitive and urinary effects, is not well characterized in controlled trials.
  • Most mechanistic evidence comes from rodents and other animal models, with unclear translation to humans.
  • Little evidence on optimal dose, route (IV vs subcutaneous vs intranasal), and patient selection in real-world settings.
  • Populations studied are narrow (treatment-resistant depression, healthy volunteers); adolescents, older adults, and non-depression psychiatric uses are understudied.
Browse these studies in the library

Common questions

What does the research agree on about ketamine?
  • Multiple RCTs and meta-analytic data show ketamine and esketamine produce rapid antidepressant effects in treatment-resistant depression, superior to active or placebo comparators at 24 hours to 28 days.
  • Continued esketamine plus oral antidepressant reduces relapse compared with discontinuation, indicating maintenance benefit beyond acute response.
  • Ketamine rapidly reduces suicidal ideation for up to about a week, with effects partly independent of overall mood change.
  • NMDA receptor antagonism is the canonical mechanism, but AMPA activation, mTOR-dependent synaptogenesis, and hydroxynorketamine metabolites are consistently implicated across preclinical and review work.
  • Dissociative, psychotomimetic, and cognitive effects are consistently reported and are a recognized limitation on broad clinical use.
Where do studies on ketamine conflict?
  • One trial in acutely suicidal patients found antidepressant benefit at 4-24 hours that was no longer significant by day 25 and no reduction in clinician-rated suicide risk, whereas pooled individual-participant data found significant reductions in suicidal ideation up to one week.
  • Preclinical work attributes antidepressant action to NMDAR-independent hydroxynorketamine mechanisms, while other reviews retain NMDAR inhibition as central; the relative contribution remains contested.
  • Real-world observational data suggest larger quality-of-life gains with esketamine add-on, but the authors themselves caution this cannot be read as a causal effect, contrasting with the randomized evidence.
  • A mouse study failed to reproduce ketamine-induced cystitis despite high drug exposure, conflicting with the human literature on chronic ketamine misuse.
What is still unknown about ketamine?
  • Durability beyond a few weeks to months is largely unestablished; most controlled efficacy data stop at 28 days or shorter.
  • Blinding integrity is questionable given ketamine's distinctive dissociative effects, which may inflate active-placebo comparisons.
  • Long-term safety of repeated dosing, including cognitive and urinary effects, is not well characterized in controlled trials.
  • Most mechanistic evidence comes from rodents and other animal models, with unclear translation to humans.
  • Little evidence on optimal dose, route (IV vs subcutaneous vs intranasal), and patient selection in real-world settings.
  • Populations studied are narrow (treatment-resistant depression, healthy volunteers); adolescents, older adults, and non-depression psychiatric uses are understudied.
How we analyze this

This synthesis reads the 15 most-cited and 10 most recent studies whose primary subject is Ketamine, up to 25 in all. The most-cited set anchors the established evidence, and the recent set surfaces work that is too new to have gathered citations yet.

A study qualifies only when Ketamine or a known alias appears in its title or keywords, so broad reviews that mention it only in passing are left out. Each study is read from its abstract, strongest evidence first, and the summary reports the direction of the results along with any conflicts and gaps.

The full method, including what a person does and does not review, is on the methods page.

Ask your own question in the Research Synthesis Tool

Latest monthly recap: September 2026 →

4,475 articles · 1,640 from the last two years · 4,519,521 participants across 1,755 studies reporting sample size

Common study designs

review 856 systematic review 240 experimental study 232 observational cohort 187 randomized controlled trial 299

Ketamine research by condition and practice

Data updated

Studies whose primary subject is both Ketamine and the condition or practice, with reviews counted by the study design extracted from each abstract. Registered trials are from ClinicalTrials.gov. This maps how much research exists, not how well anything works.

Ketamine research by condition and practice: studies, meta-analyses and systematic reviews, registered clinical trials, the highest trial phase, and studies from the last two years. Most studies first.
Condition or practice Studies Meta-analyses and systematic reviews Registered trials Highest phase From the last two years
Depression 1,746 studies 208 meta-analyses and systematic reviews 317 registered trials up to Phase 4 731 from the last two years
Anxiety 198 studies 15 meta-analyses and systematic reviews 21 registered trials up to Phase 4 76 from the last two years
Addiction 143 studies 14 meta-analyses and systematic reviews 21 registered trials up to Phase 2/3 65 from the last two years
PTSD 129 studies 14 meta-analyses and systematic reviews 39 registered trials up to Phase 4 66 from the last two years
Psychedelic-assisted therapy 92 studies 14 meta-analyses and systematic reviews 16 registered trials up to Phase 4 47 from the last two years

Research volume by year

Compare topics →

3,831 studies whose primary subject is ketamine since 2002

Studies about ketamine per year, 2002 to 2026, peaking at 780 in 2025 Bar chart: one bar per year, taller where more studies were published that year. 0 400 800 2005 2010 2015 2020 2025
2026 is partial
Show the numbers
Studies about ketamine per year, 2002 to 2026, peaking at 780 in 2025
Year Studies
2002 5
2003 3
2004 3
2005 11
2006 6
2007 8
2008 18
2009 20
2010 23
2011 57
2012 26
2013 26
2014 50
2015 57
2016 96
2017 122
2018 206
2019 124
2020 157
2021 184
2022 261
2023 355
2024 518
2025 780
2026 715

Research

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Evaluating whether a therapeutic dose of ketamine exposure during adolescence influences adult vulnerability in rats to commonly abused drugs.

Psychopharmacology October 26, 2026 Jordi Jornet-Plaza, Carles Colom-Rocha, M Julia García-Fuster

Rationale Ketamine has emerged as a rapid-acting antidepressant drug for treatment-resistant depression in adults and is currently evaluated for adolescent depression. However, the long-term effects of ketamine exposure during this period of brain development remain unclear, particularly regarding addiction liability. Objectives To investigate whether repeated ketamine exposure during...

DOI: 10.1007/s00213-026-07195-5 (opens in new tab) Full text (opens in new tab) Ketamine Treatment-resistant depression Adolescence Rapid antidepressant +2

Low-dose ketamine modulates brain entropy in treatment-resistant depression: Results from two neuroimaging clinical trials.

Journal of Affective Disorders October 26, 2026 Ying-Jay Liou, Li-Kai Cheng, Wei-Chen Lin et al.

Several studies have reported entropy reductions in regions of the brain associated with affective-regulatory and reward- and motivation-related processes in patients with major depressive disorder. However, whether low-dose ketamine modulates this reduction remains unclear. We analyzed resting-state functional magnetic resonance imaging data from two single-infusion low-dose ketamine trials....

DOI: 10.1016/j.jad.2026.122673 (opens in new tab) Full text (opens in new tab) Treatment-resistant depression Amygdala Brain entropy Clinical trial +2

Esketamine-Associated Lower Urinary Tract Symptoms Suggestive of Bladder Overactivity in Treatment-Resistant Depression: A Case Report

Research Square October 23, 2026 Clara De Oliveira Lapa, Mario F Juruena, Danilo Costa Pereira et al. preprint

Abstract Background Intranasal esketamine is an approved therapy for treatment-resistant depression and is recognized for its rapid and effective antidepressant effects. Although ketamine-associated cystitis has been documented in recreational users, the urinary safety profile of therapeutic esketamine remains incompletely characterized. Functional lower urinary tract disturbances suggestive of...

DOI: 10.21203/rs.3.rs-11132874/v1 (opens in new tab) Full text (opens in new tab)

A ketamine derivative exerts enhanced antidepressant effects via adenosine signaling.

Science China. Life sciences October 22, 2026 Na Wang, Chenyu Yue, Xiaofeng Fan et al.

Ketamine exerts rapid antidepressant effects but is limited by dissociative and abuse-related side effects, highlighting the need for safer alternatives. Here, we identify 3C-DCK, a rationally designed ketamine derivative, through adenosine dynamics in the medial prefrontal cortex (mPFC). Using the GRABAdo1.0 sensor, we show that 3C-DCK elicits more potent and sustained extracellular adenosine...

DOI: 10.1007/s11427-026-3325-7 (opens in new tab) Full text (opens in new tab) Ketamine 3c-dck A1 receptor A2a receptor +4

Treatment Response Following Repeated Low-Dose Oral Ketamine in Adults with Chronic Suicidality

University of the Sunshine Coast October 22, 2026 Cyrana C. Gallay

Suicide is an urgent public health concern and a leading cause of death, globally. Chronic suicidality may be described as persistent or recurrent suicidal ideation presenting over periods of months to years. While suicidality is associated with a complex range of proximal and distal risk factors, there is no single set of clinical features accurately able to predict development. Limited...

DOI: 10.25907/01124 (opens in new tab)

Ketamine Versus Electroconvulsive Therapy for Nonpsychotic Treatment-Resistant Depression: A Cost-Effectiveness Analysis

Psychiatric Services October 22, 2026 Michael Lebenbaum, Benoit H. Mulsant, Sagar V Parikh et al.

OBJECTIVE: Electroconvulsive therapy (ECT) is a highly effective intervention for treatment-resistant depression; however, its use has been limited partly because of concerns about cognitive side effects. Evidence for the sustained (>1 month) efficacy of ketamine versus ECT for treatment-resistant depression has only recently been demonstrated. This study aimed to examine the...

DOI: 10.1176/appi.ps.20240407 (opens in new tab)

Effects of Social Isolation on the Behavior of Wistar Rats Subjected to a Ketamine-Induced Model of Schizophrenia

Bratislavské lekárske listy/Bratislava medical journal October 22, 2026 Isabela Hubbe, Ana Luísa S. Ferreira, Nicole Luiza Rizzotto et al.

Abstract This study aimed to evaluate the impact of chronic social isolation on the behavioral profile of male and female Wistar rats within a ketamine (Ket)-induced model of schizophrenia. A total of 144 adult Wistar rats (male and female) were divided into four experimental groups per sex: (1) Socialized + Saline (Sal) (Control group); (2) Socialized + Ket; (3) Isolated + Sal (Isolated...

DOI: 10.1007/s44411-026-00921-7 (opens in new tab) Full text (opens in new tab)

Suicidality during intranasal (es)ketamine treatment: A retrospective cohort study.

Journal of Affective Disorders October 21, 2026 Yamina Ehrt-Schäfer, Georgios Schoretsanitis, Erich Seifritz et al.

Intranasal (es)ketamine has shown efficacy in therapy of treatment-resistant depression (TRD). However, its effects on suicidality have not been fully elucidated. We conducted a retrospective longitudinal cohort study of 80 patients affected by TRD, treated with intranasal (es)ketamine. Suicidality was assessed using item 10 of the clinician-rated Montgomery-Åsberg Depression Rating Scale...

DOI: 10.1016/j.jad.2026.122647 (opens in new tab) Full text (opens in new tab) Esketamine Treatment-resistant depression Suicidality

What is the efficacy of low-dose ketamine for treating depression and other mental health conditions?

Zenodo (CERN European Organization for Nuclear Research) October 21, 2026 preprint

Ketamine shows moderate efficacy as a rapid-acting treatment for treatment-resistant depression, including bipolar depression, with evidence supporting its use mainly in treatment-resistant cases. Monitoring and cautious patient selection are necessary due to limited long-term safety data.

DOI: 10.5281/zenodo.23540429 (opens in new tab)

Chronic High‐Dose Ketamine Fails to Induce a Cystitis‐Like Phenotype in Mice Despite High Urinary Metabolite Levels

Neurourology and urodynamics October 21, 2026 Jill Dewez, Ashlee Caldwell, Laura Schillebeeckx et al.

ABSTRACT: Aims: Ketamine‑induced cystitis (KIC) is a severe complication of chronic ketamine misuse, yet the underlying mechanisms remain poorly understood. Established rodent models have demonstrated variable changes in voiding behavior and bladder histology, without exploring the sensory mechanisms underlying altered voiding and pain at all. This study aimed to establish a murine model of...

DOI: 10.1002/nau.70483 (opens in new tab)

Clinical trials

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