Ketamine is a powerful anesthetic that, at lower doses, rapidly relieves severe depression, reduces chronic pain, and produces altered states of consciousness. Originally developed as a surgical anesthetic in the 1960s, it has become one of the most significant breakthroughs in psychiatric treatment in decades because of its ability to improve mood within hours rather than the weeks required by traditional antidepressants.
How Ketamine Works in the Brain
Ketamine’s primary target is a receptor called NMDA, which normally responds to glutamate, the brain’s main excitatory chemical messenger. Ketamine blocks this receptor, but in an unusual way that ends up increasing brain activity rather than dampening it. Specifically, it blocks NMDA receptors on inhibitory neurons in the prefrontal cortex. These neurons normally act as brakes on surrounding brain cells. When ketamine silences the brakes, there’s a rapid surge in glutamate release that activates neighboring neurons.
This glutamate surge triggers a cascade of downstream effects. It stimulates the production of a protein called BDNF, which acts like fertilizer for brain cells, promoting the growth and strengthening of synaptic connections. Under normal conditions, NMDA receptor activity actually suppresses BDNF production. Ketamine lifts that suppression, allowing the brain to ramp up its supply. Ketamine also binds directly to BDNF’s receptor and helps keep it active at the cell surface for longer, amplifying the signal even further.
The practical result of all this chemistry is neuroplasticity: the brain’s ability to form new connections and repair damaged ones. Research shows that ketamine rapidly enhances the growth of dendritic spines (the tiny contact points between neurons) in the prefrontal cortex, with timing that matches when its mood-lifting effects kick in. This process involves dopamine signaling as well. The behavioral improvements from ketamine can be blocked by shutting down dopamine release in the prefrontal cortex and mimicked by activating the same dopamine pathways artificially.
Treating Severe Depression
Ketamine’s most celebrated medical use is for treatment-resistant depression, meaning depression that hasn’t responded to two or more standard antidepressants. A single subanesthetic intravenous dose produces antidepressant effects within hours in patients with major depressive disorder. Following that single dose, the effects can last several days to more than a week in some patients.
In clinical trials, about 27% of patients met the criteria for an antidepressant response within 24 hours of a single infusion. After a series of repeated infusions, that number climbed to 59%, with 23% achieving full remission. Among those who responded to the initial treatment course, 91% maintained their improvement with ongoing maintenance infusions. These numbers are striking for a population where, by definition, other treatments have already failed.
The typical psychiatric dose is 0.5 mg per kilogram of body weight, infused intravenously over about 40 minutes. Some patients respond to doses as low as 0.1 mg/kg, while others need up to 0.75 mg/kg. This is far below what’s used for surgical anesthesia, which is why it’s called “subanesthetic.”
Esketamine: The FDA-Approved Nasal Spray
In 2019, the FDA approved esketamine (brand name Spravato), a nasal spray derived from one of ketamine’s two mirror-image molecules. It’s approved specifically for treatment-resistant depression and, later, for major depression with suicidal thoughts. Esketamine is not something you pick up at a pharmacy and use at home. It’s available only through a restricted program that requires certified healthcare settings, direct observation by a provider during administration, and a mandatory monitoring period of at least two hours afterward. Patients must be assessed and deemed clinically stable before they can leave.
These requirements exist because of the risk of sedation, dissociation (a feeling of being detached from your body or surroundings), and, rarely, respiratory depression. In practice, this means each treatment session is a half-day commitment at a clinic or medical office.
Chronic Pain Relief
Ketamine is also prescribed off-label as a third- or fourth-line treatment for chronic pain that hasn’t responded to other therapies. Cleveland Clinic’s protocol, for example, uses 0.5 mg/kg infused over 40 minutes for five consecutive days. The drug’s pain-relieving properties stem from the same NMDA receptor blockade that drives its psychiatric effects. NMDA receptors play a central role in “wind-up,” a process where the spinal cord and brain become increasingly sensitive to pain signals over time. By blocking these receptors, ketamine can interrupt chronic pain cycles that have become self-sustaining.
Conditions commonly treated include complex regional pain syndrome, neuropathic pain, fibromyalgia, and certain types of headache disorders. Pain relief from a course of infusions can last weeks to months, though the duration varies widely between individuals.
What It Feels Like During Treatment
At the subanesthetic doses used for depression and pain, ketamine produces noticeable psychological effects that typically last 30 to 90 minutes. Most people experience some degree of dissociation, which can range from mild detachment to vivid perceptual distortions. Colors may seem brighter, sounds may feel altered, and time perception often shifts. Some people describe a floating sensation or feeling temporarily disconnected from their body.
Nausea is common. Blood pressure and heart rate usually increase during the infusion, then return to normal afterward. Because of these cardiovascular changes, esketamine is contraindicated in patients with cerebral aneurysm, a history of intracranial hemorrhage, or arteriovenous malformations. Most clinics monitor vital signs throughout the infusion and during the recovery period.
Risks of Frequent or Recreational Use
The safety profile of ketamine in supervised, low-dose clinical settings is quite different from the picture seen with frequent recreational use at higher doses. Chronic ketamine use has been associated with severe ulcerative cystitis, a painful inflammation of the bladder lining that can become debilitating. Heavy users may also develop vesicoureteral reflux (where urine flows backward toward the kidneys) and impaired kidney function. The exact mechanism behind this bladder damage isn’t fully understood, though disruptions in how nerve signals regulate bladder muscle contractions appear to play a role.
Psychological dependence is another concern with regular use. Tolerance builds with repeated exposure, meaning higher doses are needed to achieve the same effect. At recreational doses, ketamine can cause severe confusion, memory impairment, and a state known colloquially as a “k-hole,” an intense dissociative experience that can feel like complete detachment from reality. None of these risks are typical of supervised medical treatment at standard doses, but they illustrate why ketamine therapy requires careful clinical oversight.
Anesthesia: The Original Use
Ketamine remains widely used as a surgical anesthetic, particularly in settings where sophisticated cardiovascular and respiratory monitoring isn’t available. Unlike most anesthetics, ketamine does not suppress breathing or lower blood pressure, which makes it valuable in emergency medicine, battlefield surgery, pediatric procedures, and veterinary practice. At full anesthetic doses, it produces complete unconsciousness and pain relief while maintaining airway reflexes, a combination that’s rare among anesthetic agents.