Dissociatives are a class of hallucinogen, which distort perceptions of sight and sound and produce feelings of detachment – dissociation – from the environment and self. This is done through reducing or blocking signals to the conscious mind from other parts of the brain. Although many kinds of drugs are capable of such action, dissociatives are unique in that they do so in such a way that they produce hallucinogenic effects, which may include sensory deprivation, dissociation, hallucinations, and dream-like states or trances. Some, which are nonselective in action and affect the dopamine and/or opioid systems, may be capable of inducing euphoria. Many dissociatives have general depressant effects and can produce sedation, respiratory depression, analgesia, anesthesia, and ataxia, as well as cognitive and memory impairment and amnesia.
The effects of dissociatives can include sensory dissociation, hallucinations, mania, catalepsy, analgesia and amnesia. The characteristic features of dissociative anesthesia were described as catalepsy, amnesia and analgesia. According to Pender (1972), "the state has been designated as dissociative anesthesia since the patient truly seems disassociated from his environment." Bonta (2004) described dissociative anaesthesia as "... a peculiar anaesthetic state in which marked sensory loss and analgesia as well as amnesia is not accompanied by actual loss of consciousness." Both Pender (1970) and Johnstone et al. (1959) reported that patients under anaesthesia due to either ketamine or phencyclidine were prone to purposeless movements and had hallucinations (or "dreams") during and after anaesthesia. Some patients found the hallucinations euphoric while others found them disturbing.
At sub-anesthetic doses, dissociatives alter many of the same cognitive and perceptual processes affected by other hallucinogenic drugs such as mescaline, LSD, and psilocybin; hence they are also considered hallucinogenic, and psychedelic. Perhaps the most significant subjective differences between dissociatives and the classical hallucinogens (such as LSD and mescaline) are the dissociative effects, including: depersonalization, the feeling of being unreal, disconnected from one's self, or unable to control one's actions; and derealization, the feeling that the outside world is unreal or that one is dreaming.
Some dissociative drugs are used recreationally. Ketamine and nitrous oxide are club drugs. Phencyclidine (PCP or angel dust) is available as a street drug. Dextromethorphan-based cough syrups (often labeled DXM) are taken by some users in higher than medically recommended levels for their dissociative effects. Historically, chloroform and diethyl ether have been used recreationally (as was nitrous oxide, at laughing gas parties).
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