How Does Ketamine Work for Depression? The Honest Version, Including What Is Still Unsettled

Most people who ask have already answered it: ketamine regrows synapses, it acts on glutamate rather than serotonin, and that is why it works in hours, not weeks.

That version is everywhere, it fits in three sentences, and it leaves out everything the researchers flagged.

So: how does ketamine work for depression? Something happens quickly, in a way an SSRI does not, in a use the FDA considers off-label and investigational. We give these infusions in Fort Worth, and our ketamine infusion therapy page uses those two words.

If you are in crisis or thinking about harming yourself, please do not wait. Call or text 988 to reach the Suicide & Crisis Lifeline, available 24/7, or go to your nearest emergency room. For non-emergency questions, our office line is 817-659-7344.

Is ketamine FDA-approved for depression?

Not for depression. One close relative did: esketamine, sold as Spravato, one mirror-image half of the ketamine molecule. It is a nasal spray, and we do not offer it. Section 12.1 of its FDA label reads:

“The mechanism by which esketamine exerts its antidepressant effect is unknown.”

If the approved cousin’s label says “unknown,” a confident three-sentence answer is not available yet.

Ketamine itself never got that far. Its FDA-approved label, Ketalar, approved in 1970, lists anesthetic indications only. That absence is what “off-label” means.

How does ketamine work for depression? A different receptor

Standard antidepressants are named for what they do to reuptake, the recycling of neurotransmitters out of the synapse. The National Institute of Mental Health puts their timeline at “usually 4-8 weeks.”

Ketamine is not a reuptake drug. The esketamine label describes esketamine as “a non-selective, non-competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor, an ionotropic glutamate receptor,” one that opens an ion channel directly. NIMH’s 2023 science update, “Cracking the Ketamine Code,” calls NMDA “the brain’s receptor for the neurotransmitter glutamate” – one of several.

The proposed next step: blocking NMDA produces a brief rise in glutamate signaling at another receptor, AMPA, switching on cellular pathways involved in plasticity. Zanos and Gould’s 2018 Molecular Psychiatry review concludes: “Proposed mechanisms of ketamine’s action are not mutually exclusive and may act in a complementary manner.”

Most of that came from animal work. NMDA antagonism is what the drug does; whether it is why mood changes is unsettled.

Where “ketamine regrows synapses” comes from

The claim traces to a 2010 Science paper by Li and colleagues, in rats. Ketamine rapidly activated the mTOR pathway, a cell-growth signaling route, producing “increased number and function of new spine synapses in the prefrontal cortex of rats.” The authors were careful: ketamine’s antidepressant mechanisms “have not been identified,” and the new synapses “could contribute to” them. That hedge is the authors’ own, and the first thing to go when the finding gets repeated.

A 2022 Molecular Psychiatry study by Holmes and colleagues used PET imaging in 21 people, 9 healthy volunteers and 12 with depression, PTSD or both, to measure synaptic density after one infusion. The finding: “Overall, we did not find evidence of a measurable effect on SV2A density 24 h after a single administration of ketamine… despite a robust reduction in symptoms.” An exploratory analysis hinted otherwise in patients who started lower, and the authors called for replication.

So when a page says ketamine “rewires” or “regrows” your brain, you are reading a rat finding its authors hedged and human imaging has not confirmed.

Is it ketamine, or one of its breakdown products?

A 2016 Nature paper by Zanos and colleagues, in mice, reported that the breakdown of ketamine into hydroxynorketamine “is essential for its antidepressant effects.” A published challenge followed the next year. In people it has run the other way: Farmer and colleagues, in Neuropsychopharmacology in 2020, followed 34 adults with treatment-resistant depression through one infusion and found “an inverse relationship” between hydroxynorketamine concentration and antidepressant response at 3 and 7 days, “contrary to preclinical observations and our a priori hypotheses.”

Higher metabolite, weaker response: a correlation rather than a cause, but pointed the wrong way for the theory. The metabolite itself has only completed a Phase 1 safety study in healthy volunteers, reported in Clinical Pharmacology and Therapeutics in 2024.

Does ketamine work through the opioid system?

A 2018 American Journal of Psychiatry study by Williams and colleagues starts elsewhere: “ketamine produces opioid system activation.” The team gave treatment-resistant adults naltrexone, an opioid blocker, before infusions, and reported it “dramatically blocked the antidepressant but not the dissociative effects of ketamine.” That was an interim analysis: 14 enrolled, 12 completing both conditions, stopped early.

A 2025 Nature Medicine crossover study in 26 adults found naltrexone blunted both ketamine’s glutamate signal and its day-one effect on mood. A 2025 trial by Yoon and colleagues, in 65 adults with depression and alcohol use disorder, found every group improved, including the midazolam comparison group, and no separation between the two ketamine arms.

A 2025 letter by Bandeira and colleagues, three of whom co-authored the 2018 study, argues that does not settle it. Opioid receptor activation “may be mechanistically necessary, at least for the rapid antidepressant response,” they write, yet “the results reported by Yoon et al. seem to suggest the opposite.” Their explanation: a long-acting injection given days ahead is not an oral dose timed to the infusion.

Twelve completers. Twenty-six. Sixty-five. The sample sizes are the story.

What the strongest evidence actually shows

A 2021 Cochrane review covered 64 studies and 5,299 participants. It rated the 24-hour evidence for ketamine versus placebo as “very low-certainty”: ketamine and esketamine “may be more efficacious than placebo at 24 hours,” while “how these findings translate into clinical practice, however, is not entirely clear.” That is the ceiling on any honest claim about this off-label use in unipolar depression, which is all the review covered.

A 2017 American Psychiatric Association consensus statement in JAMA Psychiatry named both halves: “rapid and robust antidepressant effects” in previously treatment-resistant patients, limited by “relatively small sample sizes, lack of longer-term data on efficacy, and limited data on safety.”

When you meet a number, ask for its denominator: the most-quoted response rate traces to a 2006 trial by Zarate and colleagues, where 71% of the 17 people given ketamine responded the day after one infusion.

Getting the diagnosis right comes first

Every study above enrolled people with unipolar depression. Bipolar depression can look identical inside a single office visit, and the distinction changes what gets prescribed. Treatment there usually leans on a mood stabilizer, partly because an antidepressant running on its own can provoke mania or hypomania. If anyone has ever raised bipolar disorder with you, say so before the conversation turns to infusions.

What this changes for you

In our office an infusion runs about 40 minutes plus a monitored recovery period, and written consent can be withdrawn at any point, including during it. Before we schedule a course, we say what this article says: a substantial proportion of treatment-resistant patients benefit, not everyone responds, and improvements are often short-term, commonly around two weeks, with individual variation. This is a procedure, not a prescription. All of it is off-label, FDA-investigational use inside a broader plan for treatment-refractory depression.

What are the risks, and who should not have ketamine?

Ketamine is not a low-stakes molecule. The anesthetic label lists it as a Schedule III controlled substance and contraindicates it in patients “for whom a significant elevation of blood pressure would constitute a serious hazard.” Rises in blood pressure and heart rate are frequent but transient, so vital signs are watched throughout. Dissociation, the feeling of being detached from your body or surroundings, is expected rather than rare, and part of why this happens in an office with staff present.

The short-term effects we talk through include dizziness, nausea, temporary increases in blood pressure, vivid dreams or perceptual changes, confusion, mood changes, or increased libido. They usually start during or soon after the infusion and often ease within about 80 minutes, though longer for some.

Because of the sedation and dissociation, a responsible adult 18 or older has to bring you, stay on site in the waiting area, and drive you home. Leaving alone, by rideshare or taxi, or with a driver who did not stay onsite, is not permitted.

Whether ketamine is reasonable for you depends on your blood pressure, cardiac history, substance use history, and what else you take. That is a conversation, not a web page.

Frequently asked questions

Is ketamine approved for depression?
No. The Ketalar label carries anesthetic indications only, so use for depression is off-label and considered investigational by the FDA. Esketamine, the nasal spray sold as Spravato, is FDA-approved for treatment-resistant depression in adults, and separately for depressive symptoms in major depressive disorder with acute suicidal ideation or behavior. A different medication by a different route, and we do not offer it.

Why does ketamine work faster than antidepressants, if it does?
The speed itself is documented. NIMH’s 2023 science update notes that “while established antidepressants could take over a month to work, intravenous ketamine worked within hours.” Why it works that fast is the unsettled part. The leading explanation is NMDA antagonism and downstream AMPA signaling rather than reuptake, but that is a hypothesis rather than a settled finding, in a use that is off-label and investigational.

Does ketamine really regrow synapses?
That comes from a 2010 rat study in Science whose authors wrote only that the new synapses “could contribute to” the antidepressant effect. Human PET imaging in 2022 found no measurable effect on synaptic density 24 hours after an infusion, though in only 21 people, most of whom were not depressed. Treat “regrows” and “rewires” as marketing language.

Is ketamine better than my SSRI?
That is not a question the evidence answers. A different mechanism is not a better one, and the 2021 Cochrane review rated the 24-hour ketamine evidence as very low certainty. Diagnosis matters too: if the depression is bipolar, an SSRI without a mood stabilizer carries a risk the other kind does not, a switch upward into mania or hypomania. Do not start, stop or change an antidepressant based on an article; ask your prescriber, who knows your whole depression plan.

The bottom line

Intravenous ketamine for depression is off-label and FDA-investigational, and the mechanism is unsettled. What is reasonably well supported: it acts on the glutamate system rather than on reuptake, and benefit, when it comes, is often short-term. What is not established is why: the metabolite hypothesis has never been tested for efficacy in people, and the opioid findings conflict across trials of twelve, twenty-six and sixty-five. “It acts through a different system than an SSRI does” is well supported. “We know how it relieves depression” is not.

Talk with us

If you are in Fort Worth or the surrounding North Texas area and what you have read here sounds familiar, we would be glad to talk it through with you. The Institute for Advanced Psychiatry is an outpatient practice at 6800 Harris Parkway, Suite 100, treating adults 18 and older. You can request an appointment or call 817-659-7344.

If you are in crisis or thinking about harming yourself, please do not wait for an appointment. Call or text 988 to reach the Suicide & Crisis Lifeline, available 24/7, or go to your nearest emergency room.

Sources

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Medical disclaimer

This article is for general education and is not medical advice, a diagnosis, or a treatment recommendation for any individual. Reading it does not create a physician-patient relationship. Treatment decisions, including whether any medication or procedure is appropriate for you, should be made with a qualified clinician who knows your history. Do not start, stop, or change a psychiatric medication without talking to your prescriber. If you are experiencing a medical or mental health emergency, call 911 or 988.