Physiological Effects

Ketamine has been studied extensively in humans. It is a noncompetitive N-methyl-D-aspartate (NMDA) antagonist (Curran & Monaghan, 2001). Recreational users of ketamine report feeling anesthetized and sedated in a dose-dependent manner (Krystal et al., 1994). Ketamine can influence all modes of sensory function (Garfield et al., 1994; Oye, Paulsen, & Maurset, 1992). At typical dosages, ketamine distorts sensory stimuli, producing illusions (Garfield et al., 1994). In higher than typical dosages, hallucinations and paranoid delusions can occur (Malhotra et al., 1996).

Ketamine substantially disrupts both attention and learning. In human research subjects, ketamine affects the ability to modify behavior, to learn new tasks, and to remember (Curran & Monaghan, 2001; Krystal et al., 1994). The recreational dosage of ketamine is approximately 0.4 mg/kg, and the anesthetic dosage is almost double that. The median lethal dose (LD50) is nearly 30 times the anesthetic dosage, which makes overdose from ketamine very rare.

One dose of ketamine creates a "trip" that lasts about 1 hour (Delgarno & Shewan, 1996). Larger doses last longer and have a more intense effect (Malhotra et al., 1996). The user feels physical tingling, followed by a feeling of removal from the outside sensory world. Tolerance develops rapidly to ketamine, and dependence, though rare, is well known. Flashbacks have been reported, and their incidence may be higher than with many other hallucinogens (Siegel, 1984). Ketamine works in a dose-dependent fashion. Mild doses involve an autistic stare and a paucity of thinking. Higher doses result in the K-hole phenomenon, which is characterized by social withdrawal, autistic behavior, and an inability to maintain a cognitive set. Such individuals may be described as zombie-like (Gay Men's Health Crisis, 1997).



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