A major depressive episode can feel like standing in a room with no doors. Antidepressants may take four to six weeks to show results—and for roughly one-third of people living with depression, those medications never work adequately. For anyone experiencing suicidal thoughts during that wait, every day carries weight.
A systematic review and meta-analysis published in JAMA Psychiatry in May 2026 now offers some of the strongest evidence to date that intravenous (IV) ketamine—an anesthetic medication used off-label at sub-anesthetic doses—can significantly reduce both depressive and suicidal symptoms in as little as four hours.
Here’s what the research found, what it means for people exploring treatment options, and what to consider before taking a next step.
What the JAMA Psychiatry Meta-Analysis Found
The study, led by Sung Ryul Shim, PhD, with corresponding author Taeho Greg Rhee, PhD, at institutions including Harvard, Yale, and the University of Toronto, analyzed 26 randomized controlled trials (RCTs) involving 1,166 people experiencing a major depressive episode (MDE). Of those, 626 received IV ketamine and 540 served as control participants.
The researchers measured two categories of outcomes: depressive symptoms and suicidal symptoms. What they found stood out for both the magnitude and the speed of the effects.
Depressive symptom reductions
A single IV ketamine infusion produced statistically significant reductions in depressive symptoms compared to control conditions at multiple time points:
- 4 hours after infusion: standardized mean difference (SMD) of −1.74
- 24 hours: SMD of −1.15
- 3 days: SMD of −0.97
- 1 week: SMD of −0.89
Repeated ketamine infusions showed a significant reduction at the end of treatment, with an SMD of −0.81.
To put those numbers in context: in clinical research, an SMD above 0.8 is generally considered a “large” effect. The four-hour result (−1.74) sits well beyond that threshold—suggesting that IV ketamine may produce a substantial shift in depressive symptoms faster than any currently available antidepressant.
Suicidal symptom reductions
For suicidal symptoms, the results were similarly meaningful:
- 24 hours after a single infusion: SMD of −0.69
- 1 month after a single infusion: SMD of −0.70
- End of treatment with repeated infusions: SMD of −0.72
These are moderate-to-large effect sizes. The persistence of a significant reduction one month after a single infusion stands out—it suggests that IV ketamine may offer more than a temporary reprieve for some individuals experiencing suicidal ideation.
As Dr. Elisabet Domínguez, a psychologist and doctor of pharmacology at Hospital de Sant Pau in Barcelona, noted in her expert commentary: “This is clinically very relevant, as no currently available treatment acts this quickly in situations of acute suicidal risk.”
Why This Meta-Analysis Matters
Individual studies of IV ketamine have shown promising results for years. What makes this publication different is the breadth and rigor of the analysis.
A meta-analysis pools data from multiple trials to generate a more precise estimate of a treatment’s true effect. By combining 26 RCTs—the gold standard in clinical research—across more than 1,100 participants, Shim, Rhee, and colleagues produced what experts at the Science Media Centre described as “a systematic review and meta-analysis of high methodological quality.”
Several factors give these findings particular weight:
- Multiple time points measured. Rather than reporting a single outcome, the researchers tracked symptom changes at 4 hours, 24 hours, 3 days, 1 week, and 1 month—painting a more granular picture of how quickly IV ketamine acts and how long those effects may persist.
- Both depressive and suicidal symptoms assessed. Many ketamine studies focus exclusively on depression severity. This meta-analysis also examined suicidal ideation, which is critical given the urgency of suicidal crises.
- Published in JAMA Psychiatry. This is one of the highest-impact, peer-reviewed journals in psychiatry. Publication here means the evidence passed rigorous editorial and peer review.
What the Study Says About Safety
Safety data from the meta-analysis were reassuring but measured. The most commonly reported side effects—headache, numbness, dissociation (a temporary feeling of being detached from your body or surroundings), nausea, dizziness, and visual disturbances—were transient and resolved within hours of the infusion.
Rarer serious adverse events, including hospitalizations and deaths, were reported in some trials. However, the researchers noted that these events were unrelated to the ketamine interventions themselves.
This tracks with the broader clinical picture: when administered at sub-anesthetic doses (typically 0.5 mg/kg) under medical supervision with appropriate monitoring, IV ketamine has a well-characterized and manageable side-effect profile.
That said, medical screening matters. Not everyone is a candidate for ketamine therapy. People with uncontrolled high blood pressure, certain cardiac conditions, active psychosis, or a history of substance use disorder require careful evaluation. A thorough medical intake—including psychiatric assessment and review of current medications—is a standard part of responsible ketamine care.
IV Ketamine vs. Other Forms: Why the Route of Administration Matters
This meta-analysis focused specifically on intravenous ketamine—not nasal sprays, lozenges, or at-home oral formulations.
IV administration offers distinct clinical advantages. The medication enters the bloodstream directly, which allows clinicians to control the dose with precision and make real-time adjustments. This level of control is part of what makes IV ketamine well-suited for medically supervised settings, where heart rate, blood pressure, and oxygen levels are monitored throughout the infusion.
The FDA has approved esketamine (Spravato®), a nasal spray version of the ketamine molecule, for treatment-resistant depression and major depressive disorder with suicidal ideation. IV ketamine (using the racemic form of the molecule) remains an off-label treatment—and it is the form with the most extensive research base, including all 26 trials in this meta-analysis.
At-home or intranasal options may be appropriate for some individuals, but they can be less predictable in terms of absorption and dosing. When the clinical priority is rapid, controlled symptom relief—especially for people in acute distress—IV ketamine in a supervised clinical setting offers the greatest precision.
What the Study Doesn’t Tell Us
The authors were transparent about what remains unknown. The most significant limitation: longer-term outcomes are not well established.
The meta-analysis confirmed that IV ketamine can produce rapid, significant relief during the acute phase of a major depressive episode. But most of the included trials followed participants for days to weeks—not months or years.
This raises important questions that future research will need to address:
- How long do the benefits of IV ketamine typically last after treatment ends?
- What is the ideal frequency and number of infusions for sustained improvement?
- Are there subgroups of people who respond better or worse to ketamine treatment?
These open questions are part of why preparation and integration—the therapeutic work that surrounds the ketamine experience—may play such an important role in translating acute symptom relief into lasting change. The infusion creates an opening; what happens during and after that opening can shape how durable the benefits become.
How IV Ketamine Works in the Brain
Ketamine works through a fundamentally different mechanism than traditional antidepressants like SSRIs (selective serotonin reuptake inhibitors), which primarily target the serotonin system and typically need weeks to take effect.
IV ketamine blocks NMDA (N-methyl-D-aspartate) receptors in the brain, leading to a surge of glutamate—the brain’s primary excitatory neurotransmitter. That glutamate surge triggers a cascade of effects, including the release of brain-derived neurotrophic factor (BDNF), which supports neuroplasticity: the brain’s ability to form new neural connections and pathways.
What does neuroplasticity mean in practice? The brain may become temporarily more flexible—more capable of forming new patterns of thought and response. Researchers at Weill Cornell Medicine have described this process as “cortical reawakening,” where ketamine briefly reactivates prefrontal cortex cells that have been suppressed by chronic stress.
This neuroplastic window may help explain why preparation and integration—therapeutic support before and after infusions—can be so valuable. When the brain is in a more receptive state, the insights and emotional processing that occur during and after treatment may be more likely to take hold.
What This Means If You’re Considering Ketamine Therapy
If you or someone you care about has been living with treatment-resistant depression or is struggling with suicidal thoughts, this meta-analysis adds to a growing body of evidence that IV ketamine may offer meaningful, rapid relief.
A few things worth keeping in mind:
- IV ketamine is not a first-line treatment. It’s typically considered after other approaches—therapy, medication trials, or both—haven’t provided adequate relief.
- Medical supervision is important. The safety profile demonstrated in this meta-analysis reflects clinical settings where dosing, monitoring, and follow-up care are standard practice.
- Preparation and integration support the process. Ketamine is a catalyst, not a cure-all. The therapeutic context around the infusion—setting intentions, processing experiences, developing new coping strategies—can help extend and deepen the benefits.
- One infusion can help, and a series may support more sustained improvement. The meta-analysis showed that both single and repeated infusions produced significant results, with repeated infusions maintaining meaningful reductions through the end of treatment.
Frequently Asked Questions
How quickly does IV ketamine work for depression?
According to the 2026 JAMA Psychiatry meta-analysis by Shim, Rhee, and colleagues, a single IV ketamine infusion produced significant reductions in depressive symptoms within four hours, with effects persisting through one week. This is considerably faster than traditional antidepressants, which may take four to six weeks.
Is IV ketamine safe?
In the 26 randomized controlled trials reviewed in the meta-analysis, the most common side effects—headache, dissociation, nausea, and dizziness—were temporary and resolved within hours. Serious adverse events were rare and unrelated to ketamine. IV ketamine should always be administered under medical supervision with proper screening and monitoring.
How long do the effects of IV ketamine last?
The meta-analysis showed significant reductions in suicidal symptoms lasting up to one month after a single infusion. For depressive symptoms, significant effects were measured through one week. Repeated infusions showed sustained benefits at the end of the treatment period. Longer-term outcomes beyond these study periods are still being investigated.
What is the difference between IV ketamine and Spravato (esketamine)?
IV ketamine uses the racemic form of the ketamine molecule and is administered intravenously as an off-label treatment. Spravato (esketamine) is an FDA-approved nasal spray that uses only one form of the molecule. The JAMA Psychiatry meta-analysis specifically studied IV ketamine, which allows clinicians to control dosing precisely and monitor responses in real time.
Who is a good candidate for IV ketamine therapy?
IV ketamine may be appropriate for adults living with treatment-resistant depression—generally defined as depression that hasn’t responded adequately to two or more medication trials—or those experiencing suicidal ideation. A comprehensive medical evaluation, including psychiatric assessment and medication review, is part of determining eligibility.
If you’re exploring whether IV ketamine therapy might be right for you, our care team is here to help you understand your options. Book a consultation to learn more about what to expect and whether this approach could support your path forward.
