Ketamine is a fast-acting dissociative anesthetic and analgesic used in human and veterinary medicine. It produces sedation, pain relief, and a characteristic sense of detachment from the body and surroundings. In controlled settings it is a valuable tool for short procedures, emergency care, and certain psychiatric treatments. Outside medical use, ketamine is sometimes used recreationally for its dissociative and hallucinogenic effects.

Pharmacology and mechanism of action

Ketamine is notable for antagonising the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors, which reduces excitatory neurotransmission and contributes to analgesia, sedation, and dissociation. It also has effects on other neurotransmitter systems and can transiently increase heart rate and blood pressure through sympathetic stimulation. Ketamine is commonly supplied as a racemic mixture; the S‑enantiomer (esketamine) has been developed separately for some medical uses.

Medical uses and formulations

Clinically, ketamine is used for:

  • Induction and maintenance of anesthesia for short procedures, particularly when maintaining airway reflexes and cardiovascular stability is important (anesthetic practice).
  • Analgesia for acute pain in emergency and perioperative settings, often as part of multimodal pain management.
  • Bronchodilation in acute reactive-airway events when other agents are unsuitable.
  • Treatment-resistant depression and acute suicidal ideation in the form of supervised intranasal esketamine and intravenous low‑dose protocols in specialised settings.

Available formulations include injectable solutions for intravenous or intramuscular use and approved intranasal preparations for specific psychiatric indications. Oral and sublingual preparations are used in some settings but have more variable absorption. Illicit markets may supply powdered, crystalline, or tablet forms that are not quality-controlled.

Routes of administration and clinical considerations

Rapid effects are usually obtained via intravenous or intramuscular injection. Intranasal delivery is used for approved psychiatric applications and for some emergency care where injections are impractical. Oral and rectal administration yield lower and less predictable plasma levels. Dosing, monitoring, and the clinical environment differ substantially between anesthesia, analgesia, and psychiatric therapy; supervision and resuscitation equipment should be available when ketamine is administered at sedating doses.

Psychological and perceptual effects

At subanesthetic doses, ketamine commonly produces altered perception, distortions of time and space, and a sense of detachment from the self and surroundings. These experiences can range from mild dissociation to intense, dreamlike states and frank hallucinations. Clinical literature and patient reports describe a range of responses; for general information see resources on hallucinatory experiences. In people with a history of psychotic disorders, ketamine may exacerbate symptoms and is used cautiously or avoided.

Adverse effects, risks, and long-term harms

Short-term effects include dizziness, nausea, vomiting, confusion, and transient increases in heart rate and blood pressure. Respiratory depression is less common at typical sedative doses than with some other anesthetics but can occur, especially when combined with other depressant drugs. Emergence reactions—distressing dreams, agitation, or confusion on waking—occur in a minority of patients.

With repeated, heavy recreational use, some people develop persistent urinary tract and bladder problems (often described as cystitis or ulcerative cystitis), chronic abdominal pain, and cognitive or memory difficulties. Tolerance and psychological dependence can develop; management of problematic use follows substance‑use treatment principles. Because of these harms, ketamine is regulated as a controlled substance in many jurisdictions.

Interactions and contraindications

Ketamine’s stimulating cardiovascular effects can be undesirable in people with uncontrolled hypertension, unstable cardiac disease, or certain aneurysmal vascular conditions. It should be used with caution in those with a history of psychosis. Concurrent use of central nervous system depressants (alcohol, benzodiazepines, opioids) increases the risk of respiratory depression and profound sedation. Decisions about use in pregnancy and breastfeeding weigh potential benefits against uncertain risks and are made case by case.

Developed in the 1960s as a shorter-acting dissociative anesthetic, ketamine was adopted for anesthesia, emergency, and battlefield medicine because of its safety profile in certain settings and its preservation of airway reflexes. Recreational misuse expanded in later decades, with reports of illicit circulation in various regions including early circulation along the West Coast of the United States before wider spread (regional histories). In recent years, medical interest has grown around rapid-acting antidepressant effects, prompting new clinical protocols and regulatory pathways for supervised use.

Safer use and harm reduction

When used medically, ketamine should be given by trained personnel in appropriate settings. For people who use ketamine outside medical supervision, harm-reduction advice includes avoiding mixing with other depressants, using in company rather than alone, starting with low amounts if choosing to use, avoiding frequent or high-dose use to reduce bladder and cognitive risks, not driving after use, and seeking medical attention for concerning symptoms such as urinary pain or breathing difficulty. For authoritative clinical guidance and further reading see specialist resources.