etamine (also known as ket, K, special K, kitty, and others) is a classical dissociative substance of the arylcyclohexylamine class. It is one of the most well-known and widely-used dissociatives, a diverse group that includes phencyclidine (PCP), methoxetamine (MXE), dextromethorphan (DXM), and nitrous oxide. It principally acts as an NMDA receptor antagonist; however, its precise mechanism is poorly understood.

Ketamine was developed in 1963 by Parke-Davis Laboratories as a replacement for the surgical anesthetic phencyclidine (PCP). It became available by prescription in 1969 under the name Ketalar.[5] Today, ketamine is widely used in human and veterinary medicine, primarily for general anesthesia for surgical procedures.[citation needed] Recreational use is associated with dance parties, electronic dance music, and the club and rave scenes.[citation needed]

Subjective effects include motor control loss, internal hallucinations, conceptual thinking, euphoria, and dissociation. Dissociation is a complex mental state characterized by perceptual distortions and feelings of detachment from the environment and one's self. Ketamine's effects are similar to dissociatives like PCP and DXM but with a shorter duration and rapid onset. The effects of ketamine are highly dose-dependent. At lower doses, users report disinhibition and relaxation effects similar to those of alcohol. Higher doses exceeding a certain threshold colloquially known as a "k-hole") are capable of inducing a trance-like state that is commonly described as an out-of-body or near-death experience.

Ketamine is considered to have moderate to high abuse potential and the health effects of chronic use are not well-known. There is significant evidence that abuse causes bladder and urinary tract dysfunction.[6] Additionally, some studies have found cognitive deficits in chronic users, which suggests it may have neurotoxic properties.[citation needed] As a result, it is highly advised to use harm reduction practices if using this substance.