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|Section2= |Section3= |Section4= }} Psilocybin ( ) is a naturally occurring psychedelic compound produced by more than 200 species of mushrooms, collectively known as psilocybin mushrooms. The most potent are members of the genus ''Psilocybe'', such as ''P. azurescens'', ''P. semilanceata'', and ''P. cyanescens'', but psilocybin has also been isolated from about a dozen other genera. As a prodrug, psilocybin is quickly converted by the body to psilocin, which has mind-altering effects similar, in some aspects, to those of LSD, mescaline, and DMT. In general, the effects include euphoria, visual and mental hallucinations, changes in perception, a distorted sense of time, and spiritual experiences, and can include possible adverse reactions such as nausea and panic attacks. Imagery found on prehistoric murals and rock paintings of modern-day Spain and Algeria suggests that human usage of psilocybin mushrooms dates back thousands of years. In Mesoamerica, the mushrooms had long been consumed in spiritual and divinatory ceremonies before Spanish chroniclers first documented their use in the 16th century. In a 1957 ''Life'' magazine article, American banker and ethnomycologist described his experiences ingesting psilocybin-containing mushrooms during a traditional ceremony in Mexico, introducing the drug to popular culture. Shortly afterward, the Swiss chemist Albert Hofmann isolated the active principle psilocybin from the mushroom ''Psilocybe mexicana''. Hofmann's employer Sandoz marketed and sold pure psilocybin to physicians and clinicians worldwide for use in psychedelic psychotherapy. Although the increasingly restrictive drug laws of the late 1960s curbed scientific research into the effects of psilocybin and other hallucinogens, its popularity as an entheogen (spirituality-enhancing agent) grew in the next decade, owing largely to the increased availability of information on how to cultivate psilocybin mushrooms. Some users of the drug consider it an entheogen and a tool to supplement practices for transcendence, including meditation and psychonautics. The intensity and duration of the effects of psilocybin are variable, depending on species or cultivar of mushrooms, dosage, individual physiology, and set and setting, as was shown in experiments led by Timothy Leary at Harvard University in the early 1960s. Once ingested, psilocybin is rapidly metabolized to psilocin, which then acts on serotonin receptors in the brain. The mind-altering effects of psilocybin typically last from two to six hours, although to individuals under the influence of psilocybin, the effects may seem to last much longer, since the drug can distort the perception of time. Psilocybin has a low toxicity and a relatively low harm potential, and reports of lethal doses of the drug are rare. Several modern bioanalytical methods have been adapted to rapidly and accurately screen the levels of psilocybin in mushroom samples and body fluids. Since the 1990s, there has been a renewal of scientific research into the potential medical and psychological therapeutic benefits of psilocybin for treating conditions including obsessive-compulsive disorder (OCD), cluster headaches, and anxiety related to terminal cancer.〔(【引用サイトリンク】 title=The Trip Treatment: Research into psychedelics, shut down for decades, is now yielding exciting results ) 〕 Possession of psilocybin-containing mushrooms has been outlawed in most countries, and it has been classified as a scheduled drug by many national drug laws. ==Effects== The effects of psilocybin are highly variable and depend on the mindset and environment in which the user has the experience, factors commonly referred to as set and setting. In the early 1960s, Timothy Leary and colleagues at Harvard University investigated the role of set and setting on the effects of psilocybin. They administered the drug to 175 volunteers from various backgrounds in an environment intended to be similar to a comfortable living room. Ninety-eight of the subjects were given questionnaires to assess their experiences and the contribution of background and situational factors. Individuals who had experience with psilocybin prior to the study reported more pleasant experiences than those for whom the drug was novel. Group size, dosage, preparation, and expectancy were important determinants of the drug response. In general, those placed in groups of more than eight individuals felt that the groups were less supportive, and their experiences were less pleasant. Conversely, smaller groups (fewer than six individuals) were seen as more supportive. Participants also reported having more positive reactions to the drug in those groups. Leary and colleagues proposed that psilocybin heightens suggestibility, making an individual more receptive to interpersonal interactions and environmental stimuli.〔 These findings were affirmed in a later review by Jos ten Berge (1999), who concluded that dosage, set, and setting were fundamental factors in determining the outcome of experiments that tested the effects of psychedelic drugs on artists' creativity.〔 After ingesting psilocybin, a wide range of subjective effects may be experienced: feelings of disorientation, lethargy, giddiness, euphoria, joy, and depression. About a third of users report feelings of anxiety or paranoia.〔 Low doses of the drug can induce hallucinatory effects. Closed-eye hallucinations may occur, in which the affected individual sees multicolored geometric shapes and vivid imaginative sequences.〔 Some individuals report experiencing synesthesia, such as tactile sensations when viewing colors.〔Ballesteros ''et al''. (2006), (p. 175. )〕 At higher doses, psilocybin can lead to "Intensification of affective responses, enhanced ability for introspection, regression to primitive and childlike thinking, and activation of vivid memory traces with pronounced emotional undertones".〔 Open-eye visual hallucinations are common, and may be very detailed although rarely confused with reality.〔 A 2011 prospective study by Roland R. Griffiths and colleagues suggests that a single high dosage of psilocybin can cause long-term changes in the personality of its users. About half of the study participants—described as healthy, "spiritually active", and many possessing postgraduate degrees—showed an increase in the personality dimension of openness (assessed using the Revised NEO Personality Inventory), and this positive effect was apparent more than a year after the psilocybin session. According to the study authors, the finding is significant because "no study has prospectively demonstrated personality change in healthy adults after an experimentally manipulated discrete event."〔 Although other researchers have described instances of psychedelic drug usage leading to new psychological understandings and personal insights,〔 it is not known whether these experimental results can be generalized to larger populations.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Psilocybin」の詳細全文を読む スポンサード リンク
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