One ketamine infusion cut suicidal symptoms within a day, a 26-trial pooling finds

Intravenous ketamine is not FDA-approved for depression or suicidal ideation, yet its off-label use for exactly these purposes has expanded substantially over the past decade, outpacing the accumulation of definitive evidence. A systematic review and meta-analysis published this week in JAMA Psychiatry consolidates two decades of randomized trial data to quantify what's actually been shown [s1].

The design

Researchers systematically searched PubMed, PsycInfo, the Cochrane Library, and Embase from database inception through 7 November 2025, without language restrictions [s1]. Eligible studies were randomized clinical trials with a diagnosed major depressive episode, comparing intravenous ketamine against a control (such as saline or midazolam), with suicidal and depressive symptoms as efficacy outcomes [s1]. Effect sizes were calculated as Hedges g standardized mean differences using random-effects models, with subgroup analyses examining single-dose versus repeated-dose ketamine [s1]. Twenty-six randomized trials comprising 1,166 patients (626 receiving ketamine, 540 controls) met inclusion criteria [s1].

What it found

For suicidal symptoms specifically, a single ketamine infusion produced significantly lower symptom scores than controls at 24 hours (standardized mean difference −0.69, 95% CI −0.98 to −0.40) and at one month (−0.70, 95% CI −1.17 to −0.24) [s1]. Repeated ketamine infusions showed a similar-sized reduction in suicidal symptoms by the end of treatment (−0.72, 95% CI −1.00 to −0.43) [s1].

For depressive symptoms more broadly, the effect was largest immediately and gradually attenuated over time: standardized mean differences of −1.74 at 4 hours, −1.15 at 24 hours, −0.97 at 3 days, and −0.89 at one week after a single infusion, with a smaller but still significant −0.81 reduction by the end of treatment with repeated infusions [s1]. Reported serious adverse events, including hospitalizations and deaths, were judged unrelated to the ketamine interventions, and other adverse events, like headache, were transient and resolved during the trials [s1].

Reading the effect sizes in context

A standardized mean difference (Hedges g) of −1.74 at 4 hours for depressive symptoms is an unusually large effect size by the standards typically seen in psychiatric drug trials, where effects in the 0.3–0.5 range are far more common — reflecting ketamine's well-documented speed of onset relative to conventional antidepressants, which typically take weeks. The pattern of gradually shrinking effect sizes over time (from −1.74 at 4 hours down to −0.81 by end of repeated treatment) tells its own story: ketamine's benefit is real and substantial in the acute window but diminishes as time passes, consistent with the drug's known pharmacological profile as a rapid-acting but not necessarily durable intervention on its own.

Why the suicidal-symptom finding at one month is the more clinically significant result

The 24-hour finding for suicidal symptoms confirms what's already fairly well established about ketamine's rapid onset. The one-month persistence of a significant reduction (−0.70) is the more clinically meaningful addition here, since acute suicide risk reduction that evaporates within days would be of limited use for sustained crisis management — a one-month window, while still short of long-term, offers more time for other interventions (therapy, medication adjustment, safety planning) to take further effect.

What this doesn't establish

The study's own authors state directly that "longer-term outcomes are not well established" [s1] — this meta-analysis's evidence base runs out at the one-month mark for suicidal symptoms and doesn't speak to what happens with continued ketamine use over months or years, optimal dosing intervals for maintenance, or long-term safety with repeated use, an increasingly relevant question given how ketamine clinics are already administering repeated treatments in practice ahead of that longer-term evidence. Twenty-six trials pooling 1,166 patients, while a meaningful evidence base, still represents individual trials that likely varied in dosing protocols, patient populations, and specific ketamine formulations (racemic ketamine versus esketamine, for instance, though the abstract doesn't specify this breakdown), introducing heterogeneity the topline pooled numbers may not fully capture.

What to watch

Longer-term follow-up data beyond one month, and further clarification of optimal maintenance dosing protocols now that this analysis has established the acute and short-term evidence base more rigorously. Intravenous ketamine is used off-label for depression and suicidal symptoms in the US; this article describes clinical trial evidence and is not medical advice.

Sources

1. Ketamine Infusions and Rapid Reduction of Suicidal and Depressive Symptoms in Major Depressive Episode: A Systematic Review and Meta-Analysis — JAMA Psychiatry, 1 July 2026