What Is Ketamine? A Complete Introduction to Ketamine Therapy

What Is Ketamine?

Ketamine is a dissociative anesthetic, first synthesized in 1962, that has become a rapid-acting treatment for depression, anxiety, and chronic pain when used at low doses under medical supervision. Chemist Calvin Stevens developed it at Parke-Davis Laboratories in Detroit as a safer alternative to phencyclidine (PCP), and the U.S. Food and Drug Administration approved it in 1970 under the brand name Ketalar. For decades ketamine served almost exclusively as a surgical anesthetic, valued for its wide safety margin and stability at room temperature.

That picture changed over the past two decades as researchers found that low, sub-anesthetic doses of ketamine can rapidly relieve depression, anxiety, and chronic pain in patients who had not responded to conventional treatment. That discovery reshaped how psychiatry approaches treatment-resistant conditions and made ketamine one of the most studied compounds in modern mental health care.

Ketamine appears on the World Health Organization's Model List of Essential Medicines, a list of drugs the WHO considers necessary for a functioning basic health system. In the United States, it is a Schedule III controlled substance under the Controlled Substances Act, a category for drugs with an accepted medical use and a moderate potential for dependence when misused.

How Ketamine Works in the Brain

The Glutamate System

Most conventional antidepressants, including SSRIs (selective serotonin reuptake inhibitors) and SNRIs (serotonin-norepinephrine reuptake inhibitors), target the brain's monoamine systems, specifically serotonin, norepinephrine, and dopamine. These medications typically require four to six weeks of consistent daily dosing before patients notice meaningful improvement.

Ketamine works through a different pathway. It primarily affects the glutamate system, the brain's most abundant excitatory neurotransmitter network, by blocking NMDA receptors (N-methyl-D-aspartate receptors), a subtype of glutamate receptor found throughout the central nervous system. Our guide to how ketamine works in the brain covers this mechanism in more depth.

The Neuroplasticity Cascade

Blocking NMDA receptors on certain inhibitory neurons triggers a surge of glutamate activity that activates AMPA receptors. That cascade leads to the release of brain-derived neurotrophic factor (BDNF), a protein central to the growth and maintenance of nerve cells. BDNF then activates the mTOR signaling pathway, which drives synaptogenesis, the rapid formation of new connections between neurons.

Chronic stress and depression can weaken these connections, particularly in the prefrontal cortex and hippocampus, brain regions tied to mood regulation. Ketamine appears to help rebuild them, sometimes within hours of a single dose. Researchers consider this capacity for neuroplasticity, the brain's ability to reorganize and form new pathways, the leading explanation for ketamine's rapid effects.

Dissociative Properties

Ketamine is classified as a dissociative anesthetic. At doses used in psychiatric treatment, patients may experience mild to moderate dissociation, including a sense of detachment from the body, altered time perception, or a dreamlike state. These effects are temporary, typically lasting 30 to 90 minutes, and are managed through monitoring during sessions.

Some clinicians believe the dissociative experience itself contributes to therapeutic outcomes by giving patients a new vantage point on entrenched thought patterns. Others view dissociation mainly as a side effect rather than a mechanism of healing. Researchers have not settled the question.

Medical and Psychiatric Uses

Anesthesia and Emergency Medicine

Ketamine's original use remains significant today. Emergency departments use it for procedural sedation, field medics rely on it where monitoring equipment is limited, pediatric anesthesiologists value its safety profile, and health systems in lower-resource settings favor it for its stability at room temperature and wide safety margin.

Treatment-Resistant Depression

Interest in ketamine's psychiatric uses grew after a 2000 Yale University study found that a single low-dose intravenous infusion produced rapid antidepressant effects. Hundreds of clinical studies have followed. According to the National Institute of Mental Health, treatment-resistant depression, meaning depression that has not responded to at least two adequate trials of conventional antidepressants, affects roughly 30% of people with major depressive disorder. For many of these patients, ketamine produces noticeable improvement within hours to days rather than the weeks required by standard antidepressants. Our guide to ketamine for treatment-resistant depression covers eligibility and what a first course typically looks like.

Anxiety Disorders

Research increasingly points to ketamine as a potential option for generalized anxiety disorder, social anxiety disorder, and specific phobias. The same glutamate-mediated mechanisms behind its antidepressant effects appear relevant to anxiety circuits involving the prefrontal cortex and amygdala.

Chronic Pain

Ketamine's role in pain management predates its psychiatric use. Clinicians use it for complex regional pain syndrome (CRPS), neuropathic pain, fibromyalgia, and other conditions that resist standard analgesics. Pain-focused protocols generally involve higher doses and longer infusions than psychiatric protocols.

Other Conditions Under Study

Researchers are also studying ketamine for PTSD, OCD, bipolar depression, suicidal ideation, and substance use disorders. Evidence quality varies by condition, but early results across several psychiatric diagnoses have been encouraging.

How Ketamine Is Administered

Ketamine therapy is available through several delivery methods that differ in onset time, bioavailability, and the clinical setting required. Our ketamine treatment methods guide compares these options in more detail.

Intravenous (IV) Infusion

IV infusion is the most studied method for psychiatric use. The standard protocol delivers 0.5 mg/kg over 40 minutes, giving 100% bioavailability and precise, real-time dose control. A typical initial course runs six infusions over two to three weeks, followed by maintenance sessions spaced according to each patient's response.

Intranasal (Nasal Spray)

The S-enantiomer of ketamine, esketamine, is marketed as Spravato and received FDA approval in 2019 for treatment-resistant depression. Patients receive it as a nasal spray in certified healthcare settings, under direct supervision, with a required two-hour observation period after each dose. See our esketamine overview for dosing and eligibility details.

Oral and Sublingual

Compounded oral and sublingual formulations are increasingly prescribed through telehealth programs for at-home use. Bioavailability runs lower, about 20-30% for oral and 25-35% for sublingual, but these routes offer greater accessibility and lower per-session cost, typically under a prescribing provider's virtual monitoring.

Intramuscular (IM) Injection

IM injection sits between IV infusion and oral formulations. It reaches roughly 93% bioavailability with a faster onset than sublingual dosing, though without the real-time adjustment that IV delivery allows.

The Two Forms of Ketamine

The ketamine molecule exists as two mirror-image forms, or enantiomers.

• S-ketamine (esketamine): Binds NMDA receptors with roughly two to four times the affinity of R-ketamine. Spravato, the FDA-approved nasal spray, contains only this enantiomer.
• R-ketamine (arketamine): Currently under investigation, with preclinical and early clinical studies suggesting antidepressant activity with potentially fewer dissociative effects.

Most ketamine used in clinical practice is racemic, meaning it contains equal parts S- and R-ketamine. Whether one enantiomer offers a meaningful clinical advantage over the other remains an open research question. Our racemic ketamine vs. esketamine comparison breaks down what the current evidence shows.

Safety and Side Effects

Ketamine therapy administered under medical supervision has an acceptable safety profile across numerous clinical studies, though it carries real risks and side effects that patients should understand before starting treatment. Our safety and side effects guide and side effects breakdown cover this in more detail.

Common Side Effects

The most frequently reported effects during and shortly after treatment include dissociation, dizziness, nausea (in roughly 30-40% of patients), a transient rise in blood pressure and heart rate, blurred vision, and fatigue. These effects are typically mild to moderate and resolve within one to two hours.

Who Should Not Receive Ketamine

Contraindications include uncontrolled high blood pressure, active psychotic disorders such as schizophrenia, a current substance use disorder involving ketamine or PCP, untreated hyperthyroidism, significantly elevated intracranial pressure, and pregnancy. A thorough medical screening should precede treatment for every patient.

Long-Term Considerations

Long-term safety data on therapeutic ketamine use is still accumulating. Bladder toxicity, well documented in chronic heavy recreational users, has not shown up at standard therapeutic doses and frequencies in clinical studies so far. Cognitive effects and dependence risk at clinical doses also appear low, and researchers continue to monitor both.

Is Ketamine Legal?

In the United States, ketamine is a Schedule III controlled substance under the Controlled Substances Act, and it is legal for medical use when prescribed and administered by a licensed provider. Off-label prescribing for psychiatric conditions is a lawful, widely accepted practice, though ketamine is FDA-approved for this purpose only in its esketamine form, Spravato, for treatment-resistant depression and major depressive disorder with suicidal ideation.

Rules around telehealth prescribing, compounding pharmacy practices, and at-home administration vary by state. Confirm that any provider operates within the regulatory framework that applies where you live. Our detailed look at ketamine's legal status walks through the state-by-state considerations.

What to Know Before Considering Ketamine Therapy

Ketamine therapy is not a one-time fix, and going in with realistic expectations matters as much as finding a qualified provider. Our guide to finding a ketamine providercost breakdown, and insurance coverage guide go deeper on the logistics below.