What Is Ketamine? Therapy, Effects, and Mechanisms

Ketamine occupies a strange and consequential niche in modern medicine. It is one of the only compounds in widespread use that is simultaneously an FDA-approved anesthetic, an FDA-approved psychiatric medicine, a DEA Schedule III controlled substance, and a decades-old recreational dissociative. No other widely-used drug sits cleanly across all four statuses at once.

The details of that overlap are worth understanding carefully. Ketamine has been an anesthetic in operating rooms and emergency departments since 1970. It has been used recreationally since the 1970s under street names including "K" and "Special K." And starting in 2019, a nasal-spray form called Spravato became the first genuinely new antidepressant mechanism approved by the FDA in thirty years, an extraordinary pace for any new class of psychiatric medication.

This guide covers what ketamine is, what it does in the brain, how the FDA approval works, what happens at off-label IV clinics, what the experience is actually like, what the real risks are, and where ketamine fits in the broader landscape of psychedelic-adjacent medicine.

What Is Ketamine?

Ketamine is a synthetic arylcyclohexylamine, a class of dissociative anesthetics that also includes phencyclidine (PCP) and its close chemical relatives. Its chemical name is (RS)-2-(2-chlorophenyl)-2-(methylamino)cyclohexan-1-one, and its molecular formula is C13H16ClNO. It was synthesized in 1962 by Calvin Stevens, a medicinal chemist at the Parke-Davis Laboratories, while he was searching for a safer alternative to PCP.

The molecule is chiral, which means it exists in two mirror-image forms called enantiomers. The (S)-enantiomer is called esketamine; the (R)-enantiomer is called arketamine. Racemic ketamine, which is the form most commonly used in clinics and on the street, contains both enantiomers in equal proportions. Esketamine, the (S)-enantiomer alone, is the form that the FDA approved in 2019 for treatment-resistant depression under the brand name Spravato, developed by Janssen Pharmaceuticals as a nasal spray.

At anesthetic doses (typically 1-2 mg/kg IV or 3-8 mg/kg IM), ketamine produces a trance-like state characterized by profound analgesia, immobilization, and dissociation from the body and environment, while preserving airway reflexes and spontaneous respiration. This is why it became the anesthetic of choice in field medicine, emergency departments, and veterinary practice: it does not suppress breathing the way opiates and most general anesthetics do.

At sub-anesthetic doses (typically 0.2-0.5 mg/kg IV, or roughly 50-200 mg IM), the dissociative effects become the dominant feature. Users describe the experience as a kind of unmooring: the body can feel distant, the visual field can distort, and thought patterns become unusual without the loss of consciousness that defines the anesthetic dose range. This sub-anesthetic range is where the recreational use, the psychiatric use, and the off-label clinical use all converge.

Pharmacologically, ketamine's primary mechanism is antagonism at the NMDA (N-methyl-D-aspartate) receptor, the brain's main excitatory glutamate receptor. Blocking NMDA receptors triggers a downstream cascade that includes a transient surge in glutamate release, AMPA receptor activation, increased brain-derived neurotrophic factor (BDNF), and rapid synaptogenesis in the prefrontal cortex. It also inhibits the reuptake of serotonin, norepinephrine, and dopamine at higher doses, contributing to the mood-elevating and sympathetic-activating effects users report.

A Brief History

Calvin Stevens synthesized ketamine in 1962 at Parke-Davis while searching for a safer PCP analog. PCP had been used as an anesthetic but caused prolonged post-operative psychosis in a significant fraction of patients. Ketamine proved to have a much cleaner emergence profile and was selected for further development.

The FDA approved ketamine as an anesthetic in 1970. From 1970 onward, ketamine saw widespread use in battlefield medicine during the Vietnam War, in pediatric procedures (where its airway-preserving profile made it especially valuable), in veterinary practice, and in emergency departments around the world. The dissociative experience that recreational users later prized was known from the start, but it was considered a manageable side effect in clinical settings rather than a feature.

Recreational use grew through the 1970s, 1980s, and especially the 1990s. Ketamine became a fixture in the New York and London club scenes of the mid-1990s, where it was sold under names including "Special K," "Kit Kat," and "Vitamin K." The aesthetic of the K-hole, the dissociative state at higher doses, was both romanticized and dramatized in ways that sometimes fed stigma and sometimes fueled misunderstanding of what lower-dose clinical use looks like.

The pivot toward psychiatric medicine happened in 2000. A small but rigorous study published in Biological Psychiatry by Berman and colleagues at the Yale School of Medicine showed that a single low-dose IV infusion of ketamine produced rapid and significant antidepressant effects in patients with major depression. Effects appeared within hours, not across the weeks required for SSRIs to take hold. The sample was small (seven participants), and the study was not designed for definitive efficacy claims, but the signal was strong enough to launch two decades of follow-on research.

In March 2019, the FDA approved esketamine nasal spray (Spravato, developed by Janssen) for treatment-resistant depression. In August 2020, the indication was expanded to include major depressive disorder with acute suicidal ideation or behavior, the first time any medication had been specifically approved for that indication. The acceleration from "single-site academic finding" to "FDA approval" in nineteen years is unusually short for psychiatric drug development, and reflects the genuinely unmet medical need in treatment-resistant depression.

How It Works in the Brain

Ketamine's primary binding target is the NMDA receptor, an ionotropic glutamate receptor that mediates most fast excitatory neurotransmission in the central nervous system. By blocking NMDA receptors, ketamine reduces the excitatory tone that GABAergic interneurons normally exert on principal glutamatergic neurons. The short-term paradoxical effect is a glutamate surge: principal neurons, released from inhibition, briefly fire more.

This transient glutamate surge activates AMPA receptors (a different glutamate receptor subtype that is not blocked by ketamine). AMPA activation triggers a calcium influx into the postsynaptic neuron, which in turn releases BDNF, a neurotrophin associated with synaptic growth and plasticity. BDNF then activates TrkB receptors, which drive the synthesis of proteins needed to build and stabilize new synaptic connections. Within hours of a single infusion, increased dendritic spine density has been documented in preclinical models.

The neuroplasticity story is the leading hypothesis for ketamine's sustained antidepressant effect. Standard antidepressants (SSRIs, SNRIs) also increase BDNF, but the time course is slower because the mechanism proceeds through gradual receptor adaptation rather than direct NMDA blockade. Ketamine appears to compress what normally takes weeks into hours.

There are unresolved questions. The dissociative experience itself may be therapeutically relevant, much as the subjective psychedelic experience is thought to contribute to the psilocybin effect. Some researchers have proposed that the dissociation provides a temporary loosening of rigid cognitive and emotional patterns, allowing new perspectives to consolidate once the experience ends. This is consistent with clinical observation that the antidepressant window (typically a few days after a single infusion) does not always persist without repeated dosing.

Ketamine also engages opioid systems to a degree that has recently drawn more attention. In 2018, researchers at Stanford published findings that naltrexone pretreatment blocked ketamine's antidepressant effect in a small trial, suggesting that opioid receptor activation may be part of the mechanism. This remains an active and contested area of research.

What FDA Approval Actually Means

The 2019 Spravato approval was specifically for treatment-resistant depression (TRD), defined as major depressive disorder in patients who have failed to respond adequately to at least two different antidepressant treatments of adequate dose and duration during the current depressive episode. An adequate trial typically means six to eight weeks at a therapeutic dose. Stopping a medication in the first two weeks due to side effects, or never being titrated to therapeutic dose, may not count even when the patient feels they have "tried everything."

The 2020 expansion covered a different population: patients with major depressive disorder accompanied by acute suicidal ideation or behavior. This is the first time any medication has been specifically approved for that acute indication. The clinical rationale is that the rapid onset of ketamine's antidepressant effect offers something no other approved medication can, a meaningful reduction in suicidal thinking within hours to days.

Both approvals came with a Risk Evaluation and Mitigation Strategy (REMS) requirement. Spravato is dispensed only through certified healthcare settings. Patients cannot take it home. Each dose is self-administered in the clinic under direct medical supervision, and patients must be monitored for at least two hours afterward for dissociation, sedation, and blood pressure changes. The REMS exists because of ketamine's dissociative effects and its known abuse potential as a Schedule III substance.

For patients who qualify under the TRD definition, Spravato is now part of the standard treatment pathway rather than an experimental option. The clinical protocol typically involves twice-weekly sessions for the first four weeks, then weekly or biweekly maintenance. Insurance coverage varies considerably: some major insurers cover Spravato for TRD patients who meet documentation criteria; others require extensive prior authorization. Out-of-pocket cost per session without coverage can run several hundred dollars, making cost a real access barrier even when medical eligibility is met.

For a deeper look at the clinical research behind these approvals, how Spravato differs from off-label IV ketamine, and where it sits alongside psilocybin in the broader psychiatric pipeline, see our ketamine therapy explainer.

IV Ketamine Clinics

Alongside the Spravato approval, a separate ecosystem of off-label IV ketamine clinics has grown rapidly across the United States over the past decade. These clinics administer racemic ketamine intravenously, in many cases off-label for depression, anxiety, PTSD, and other psychiatric conditions, at doses and protocols that vary considerably between providers.

IV ketamine is not FDA-approved for depression. Ketamine is FDA-approved as an anesthetic, and physicians may prescribe it off-label for any indication they judge clinically appropriate, but there is no standardized protocol, no REMS requirement, and no specific regulatory oversight for this off-label psychiatric use.

This lack of standardization matters. Doses vary (typical range 0.5-2 mg/kg IV over 40-60 minutes), infusion rates vary, the number of initial sessions varies (six over two to three weeks is the most common protocol, but some clinics use different schedules), integration support varies, and the clinical context varies enormously. Some clinics are staffed by board-certified psychiatrists with structured preparation, supportive monitoring, and integration counseling built into the protocol. Others operate closer to infusion-mills, with minimal medical screening and limited psychological care.

Cost at off-label IV ketamine clinics typically runs $400-$800 per infusion, with an initial series of six over two to three weeks followed by maintenance sessions as needed. Insurance rarely covers this use. For patients who do not qualify for Spravato under the strict TRD criteria, or who cannot access a Spravato-certified clinic, off-label IV ketamine may be a practical option, but it requires careful vetting of the clinic's clinical standards, psychiatric oversight, and emergency protocols.

The same caveat applies to intranasal racemic ketamine dispensed at compounding pharmacies, intranasal kits distributed for home use without medical supervision, and oral ketamine prescribed by telehealth providers in some states. The therapeutic substance is the same, but the safety infrastructure around it varies far more than most patients realize.

The Experience

Effects begin within minutes of IV infusion, typically five to fifteen minutes after the start of the drip. Intramuscular onset is similar (five to ten minutes after injection). Intranasal esketamine (Spravato) onset is within ten to twenty minutes. Oral ketamine has the slowest onset, generally thirty to sixty minutes, and routes through first-pass metabolism which reduces bioavailability substantially.

The acute subjective effects at sub-anesthetic doses consistently include:

• Dissociation: A sense of distance from the body, from thoughts, or from the immediate environment. Some users describe it as floating above themselves; others describe it as the mind and body temporarily decoupling. Dissociation can range from mild and pleasant to intense and disorienting, depending on dose, route, and individual susceptibility.
• Visual and perceptual changes: Blurring, vibrant color shifts, geometric patterns with eyes closed, alterations in depth perception, and sometimes full immersive visual scenes. Visual effects at sub-anesthetic doses are typically less vivid than those reported with LSD or psilocybin, but they are real and can be more disorienting in character because the cognitive map of the experience is less familiar.
• Cognitive shifts: Loose associative thinking, slowed processing of time, difficulty sustaining linear narrative, and a sense that usual frameworks and categories no longer apply in quite the same way. Some users report meaningful cognitive insights in this window.
• Mood shifts: Rapid reduction in depressive rumination, increased emotional warmth, openness, and in some cases euphoria. The mood elevation is one of the features of the experience that has driven interest in therapeutic use.

At higher doses, the dissociative effects can intensify into what users call a "K-hole," a profound out-of-body experience with little or no connection to the immediate environment. The K-hole is real, can be disorienting even for experienced users, and has been romanticized in ways the safety literature does not support. Reports of people becoming unresponsive to verbal cues, having difficulty moving coherently, or experiencing significant distress during a K-hole are common enough to warrant taking the phenomenon seriously.

Duration of effects depends heavily on route. The IV / IM experience typically lasts one to two hours from infusion start to baseline return. Intranasal Spravato is similar, with effects resolving within approximately two hours. Oral ketamine lasts substantially longer, often four to six hours, because of slower absorption and the active metabolite norketamine's longer half-life.

After the acute experience resolves, the "coming-down" period often feels gentle rather than abrupt. Many users report a reflective, somewhat tender emotional state during the day or two following treatment, with gradual reconsolidation into ordinary consciousness.

Risks and Safety

Ketamine's safety profile is comparatively favorable at single clinical doses, but it is not trivial. The most consistently documented acute risks include:

Cardiovascular effects: Ketamine raises blood pressure and heart rate in a dose-dependent way. Patients with uncontrolled hypertension, recent cardiac events, aortic dissection, or severe heart failure are typically excluded from both Spravato and off-label IV protocols. Transient blood pressure spikes during infusion are expected and manageable in monitored settings; the risk comes from unsupervised use in individuals with underlying cardiac vulnerabilities.

Dissociation-related accidents: Dissociation at higher doses impairs motor coordination and situational awareness. Falls, near-drowning incidents (bathtubs, swimming pools), and accidents during unobserved K-hole episodes have been documented in the harm-reduction literature. This is why monitored clinical settings restrict mobility during the experience and require patients to remain seated or lying down until baseline returns.

Cystitis with chronic heavy use: Ketamine cystitis is a documented condition associated with frequent, long-term recreational use. Symptoms include urinary urgency, frequency, pelvic pain, and in severe cases, irreversible bladder dysfunction. The condition is dose- and frequency-dependent, with risk climbing sharply at use patterns beyond what any clinical protocol would prescribe. Important to note: this is not a documented risk at clinical dosing frequencies (single session, weekly maintenance, or twice-weekly Spravato).

Drug interactions: Combining ketamine with other sedating or dissociating substances, especially alcohol, benzodiazepines, or other anesthetics, increases the risk of overdose on the dissociative and respiratory-depressing dimensions. There is no classic serotonin syndrome risk the way there is with MDMA combined with SSRIs, but combining ketamine with stimulants (cocaine, methamphetamine) increases cardiovascular strain substantially.

Addiction and abuse potential: Ketamine dependence is documented in chronic recreational users, with tolerance, craving, and compulsive use patterns. Ketamine is a Schedule III controlled substance for this reason. The risk in monitored clinical use is real but small; the harm-reduction conversation about unsupervised chronic recreational use is much more concerning.

Psychological risks: As with any psychoactive compound, ketamine can precipitate or worsen psychotic episodes in people with personal or family histories of psychosis or schizophrenia with psychotic features. Clinical protocols screen for this risk.

Acute fatal overdose on ketamine alone, in adults, is rare at the doses typically encountered. Most ketamine-related deaths involve polysubstance use, contributing context like alcohol or opioids, or accident during impairment rather than direct toxicity.

Legal Status

Ketamine sits in a fundamentally different legal category from the Schedule I psychedelics. It is a Schedule III controlled substance under the United States Controlled Substances Act, classified as having currently accepted medical use with moderate-to-low dependence risk relative to Schedule II substances. Schedule III is the same tier as testosterone and certain anabolic steroids, suboxone, and codeine-containing products.

This scheduling affects the practical regulatory landscape in three ways. First, physicians can prescribe ketamine off-label for indications other than anesthesia, which is what powers the IV ketamine clinic ecosystem described earlier. Second, compounding pharmacies can legally prepare non-FDA-approved formulations of ketamine (intranasal, sublingual, oral) under federal compounding rules, though some state pharmacy boards have tightened oversight. Third, the regulatory pathway for any new ketamine-based drug is comparatively lower friction than for Schedule I compounds, which is part of why the Spravato approval timeline was achievable in 2019.

State-level ketamine regulations are less uniform. Several states have passed or are considering legislation specifically addressing ketamine telehealth, after the rise of direct-to-consumer ketamine telemedicine companies in the early 2020s. Colorado and Texas have implemented or are implementing specific prescribing requirements. The federal DEA has issued guidance that's sometimes been read as restrictive and sometimes permissive, contributing to an unsettled enforcement environment through 2025.

For the broader picture of how different psychedelic and psychedelic-adjacent substances are regulated at the state level, the US Psychedelic Laws Map is updated regularly.

Where Ketamine Fits Now

Ketamine is the only widely-used compound in the psychedelic-adjacent space that already has FDA approval for a major psychiatric indication, a fact that puts it at a unique position in the clinical landscape. Spravato for treatment-resistant depression is available now through certified clinics with insurance coverage in some cases. Off-label IV ketamine clinics operate across the country with established (if unregulated) protocols. The clinical evidence base is two decades deep.

The tradeoffs are also distinctive. Compared to MDMA, which targets serotonin and oxytocin systems and is being studied for PTSD through Phase 3 trials, ketamine acts on glutamate rather than serotonin and lives in the dissociative anesthetic class rather than the empathogen class. Compared to psilocybin, which produces a long experience with sustained remission potential from a small number of sessions, ketamine produces a short experience that often requires ongoing maintenance dosing. Each compound has its own profile, its own regulatory pathway, and its own clinical use case.

For the deeper clinical and regulatory story behind the 2019 Spravato approval, including the TRD definition, the REMS protocol, the IV clinic ecosystem, and how ketamine compares to the psilocybin pipeline, see our ketamine therapy research deep-dive. For the broader context of how ketamine fits into the psychedelic medicine landscape, see what psychedelics actually are. To compare ketamine with the other core substances side-by-side, the Compare Psychedelics hub provides a one-page reference for duration, dose, risk profile, and harm-reduction priorities.