Ketamine is a dissociative anesthetic that has been used in medicine since the 1970s and has more recently become one of the most studied treatments for severe depression. It works differently from traditional antidepressants, producing rapid changes in brain chemistry that can relieve symptoms within hours rather than weeks. Today, ketamine exists in two worlds: it remains a staple anesthetic in emergency rooms and surgical suites, and it’s increasingly used at low doses to treat psychiatric conditions that haven’t responded to other medications.
How Ketamine Works in the Brain
Most antidepressants target serotonin or related brain chemicals. Ketamine takes a completely different route. It blocks a type of receptor called NMDA, which is involved in how brain cells communicate using glutamate, the brain’s primary excitatory chemical messenger.
The process unfolds in a chain reaction. Ketamine first blocks NMDA receptors on a specific set of inhibitory brain cells. These cells normally act like brakes on surrounding neurons, so when ketamine takes them offline, the result is a burst of glutamate release. That flood of glutamate activates a second type of receptor (AMPA), which triggers a cascade of growth signals. Within one to two hours of a single dose, the brain begins producing proteins that build and strengthen connections between neurons, essentially forming new synaptic wiring in areas like the prefrontal cortex that regulate mood and cognition.
One of the key players in this process is a growth factor called BDNF, which promotes the maturation of new synaptic spines and strengthens communication between neurons. This rapid rewiring is why ketamine can produce antidepressant effects so much faster than conventional medications, which typically take four to six weeks to reach full effect.
Medical Uses for Depression
Ketamine’s psychiatric use centers on treatment-resistant depression, defined as depression that hasn’t improved after trying at least two different antidepressants. At sub-anesthetic doses, typically 0.5 mg/kg delivered intravenously over 40 minutes, ketamine can produce noticeable mood improvement within hours. Some studies have tested doses as low as 0.1 mg/kg, though 0.5 mg/kg remains the most commonly studied and used.
In 2019, the FDA approved a nasal spray called Spravato, which contains esketamine, a more potent form of ketamine. It’s approved for two specific situations: treatment-resistant depression in adults, and depressive symptoms in adults with major depression who have active suicidal thoughts or behavior. Because of risks including sedation, dissociation, and potential for misuse, Spravato is only available through a restricted program. You can’t pick it up at a pharmacy and take it at home. Instead, each dose is administered in a certified healthcare setting, and you’re monitored for at least two hours afterward.
IV ketamine clinics, which use the older generic form of the drug, operate somewhat differently. These are typically run by anesthesiologists or psychiatrists and aren’t bound by the same federal monitoring program, though protocols vary by clinic. A common approach for depression involves a series of six infusions over two to three weeks, followed by maintenance sessions spaced further apart depending on how long the effects last.
Racemic Ketamine vs. Esketamine vs. Arketamine
The ketamine molecule comes in two mirror-image forms, like left and right hands. Standard ketamine is a 50/50 mix of both, called racemic ketamine. The two halves have been separated and studied individually.
Esketamine (the S-form) binds to NMDA receptors about four times more potently than the R-form. This higher potency allows for lower doses, which was part of the rationale behind developing Spravato. However, animal research has found something surprising: arketamine (the R-form) may actually produce stronger and longer-lasting antidepressant effects with fewer dissociative side effects. Arketamine is currently being studied in clinical trials but isn’t yet approved for any use.
Use in Anesthesia and Pain Management
Ketamine was originally developed as an anesthetic and remains widely used in that role, particularly in emergency medicine, battlefield settings, and pediatric surgery. It’s valued because it doesn’t suppress breathing or blood pressure the way many other anesthetics do, making it safer in situations where monitoring equipment is limited.
For chronic pain, ketamine infusions are used at higher doses and over longer periods than in depression treatment. Guidelines suggest starting with at least 80 mg over two hours or more, since shorter infusions tend to provide relief lasting no more than 48 hours. Some protocols involve infusions of up to 100 mg over four hours daily for 10 consecutive days, with pain relief persisting for 9 to 12 weeks after the treatment course. A retrospective study of 49 patients with various chronic pain conditions found a nearly 6-point reduction on a 10-point pain scale after a median of four infusions.
Side Effects During Treatment
At the sub-anesthetic doses used for depression, the most common side effects are dissociation (a feeling of being detached from your body or surroundings), dizziness, nausea, and increases in blood pressure. These effects typically peak within the first hour and resolve within two hours, which is why the monitoring period exists. The dissociative experience can feel strange or unsettling, though some patients describe it as neutral or even pleasant.
Blood pressure increases are generally mild and temporary, but people with uncontrolled hypertension, a history of brain hemorrhage, or blood vessel abnormalities such as aneurysms are not candidates for ketamine treatment. Active psychotic disorders and current substance use disorders are also standard exclusion criteria.
Bladder Damage From Heavy or Prolonged Use
One of the more serious risks of ketamine involves the bladder, and it’s primarily a concern with frequent, heavy, or recreational use rather than supervised medical treatment. Over 25% of recreational ketamine users develop urinary symptoms, and the risk climbs with dose and frequency. Frequent users report cystitis-like symptoms (pain, urgency, frequent urination) at roughly three times the rate of infrequent users, and ketamine users overall are six times more likely to develop lower urinary tract problems than the general population.
The damage appears to be caused by ketamine and its byproducts passing through urine and directly irritating the bladder lining. This triggers inflammation, damages the protective layer of the bladder wall, and can eventually lead to scarring and a shrunken, stiffened bladder. In severe cases, surgical intervention is needed. The condition is sometimes called ketamine-induced cystitis, and it’s one of the main reasons recreational ketamine use carries risks that supervised medical use largely avoids, since clinical doses are far lower and far less frequent.
Ketamine as a Recreational Drug
Ketamine is classified as a Schedule III controlled substance in the United States, meaning it has accepted medical uses but also carries potential for misuse. Recreationally, it’s used for its dissociative and hallucinogenic effects, often at doses higher than those used in clinical settings. At very high recreational doses, users describe a state called a “K-hole,” a deeply dissociative experience that can involve vivid hallucinations and a sense of complete detachment from reality. Regular recreational use carries risks of psychological dependence, cognitive impairment, and the bladder damage described above. The profile of risk looks very different from the controlled, low-dose protocols used in medical settings, where sessions are spaced apart and doses are carefully managed.