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Psilocybin mushrooms, also known as psychedelic mushrooms, are mushrooms that contain the psychedelic compounds psilocybin and psilocin. Common colloquial terms include magic mushrooms and 'shrooms. Biological genera containing psilocybin mushrooms include Copelandia, Galerina, Gymnopilus, Inocybe, Mycena, Panaeolus, Pholiotina, Pluteus, and Psilocybe. Approximately 40 species are found in the genus Psilocybe, but Psilocybe cubensis is the most common psilocybin mushroom in subtropical areas and the black market.
Psilocybin mushrooms have likely been used since prehistoric times and may have been depicted in rock art. Many cultures have used these mushrooms in religious rites. In modern societies, they are used recreationally for their psychedelic effects.
Archaeological evidence indicates the use of psilocybin-containing mushrooms since ancient times. Several mesolithic rock paintings from Tassili n'Ajjer (a prehistoric North African site identified with the Capsian culture) have been identified by author John S. Ashley as possibly depicting the shamanic use of mushrooms, possibly Psilocybe.
Hallucinogenic species of the psilocybe genus have a history of use among the native peoples of Mesoamerica for religious communion, divination, and healing, from pre-Columbian times to the present day. Mushroom stones and motifs have been found in Mayan temple ruins in Guatemala. A statuette dating from ca. 200 AD and depicting a mushroom strongly resembling Psilocybe mexicana was found in a west Mexican shaft and chamber tomb in the state of Colima. Hallucinogenic Psilocybe were known to the Aztecs as teonanácatl (literally "divine mushroom" - agglutinative form of teó (god, sacred) and nanácatl (mushroom) in Náhuatl) and were reportedly served at the coronation of the Aztec ruler Moctezuma II in 1502. Aztecs and Mazatecs referred to psilocybin mushrooms as genius mushrooms, divinatory mushrooms, and wondrous mushrooms, when translated into English. Bernardino de Sahagún reported ritualistic use of teonanácatl by the Aztecs, when he traveled to Central America after the expedition of Hernán Cortés.
After the Spanish conquest, Catholic missionaries campaigned against the "pagan idolatry", and as a result, the use of hallucinogenic plants and mushrooms, like other pre-Christian traditions, were quickly suppressed. The Spanish believed the mushroom allowed the Aztecs and others to communicate with devils. In converting people to Catholicism, the Spanish pushed for a switch from teonanácatl to the Catholic sacrament of the Eucharist. Despite this history, in some remote areas, the use of teonanácatl has remained.
The first mention of hallucinogenic mushrooms in European medicinal literature appeared in the London Medical and Physical Journal in 1799: a man had served Psilocybe semilanceata mushrooms that he had picked for breakfast in London's Green Park to his family. The doctor who treated them later described how the youngest child "was attacked with fits of immoderate laughter, nor could the threats of his father or mother refrain him."
In 1955, Valentina and R. Gordon Wasson became the first known Caucasians to actively participate in an indigenous mushroom ceremony. The Wassons did much to publicize their discovery, even publishing an article on their experiences in Life in 1957. In 1956 Roger Heim identified the psychoactive mushroom that the Wassons had brought back from Mexico as Psilocybe, and in 1958, Albert Hofmann first identified psilocybin and psilocin as the active compounds in these mushrooms.
Inspired by the Wassons' Life article, Timothy Leary traveled to Mexico to experience psilocybin mushrooms firsthand. Upon returning to Harvard in 1960, he and Richard Alpert started the Harvard Psilocybin Project, promoting psychological and religious study of psilocybin and other psychedelic drugs. After Leary and Alpert were dismissed by Harvard in 1963, they turned their attention toward promoting the psychedelic experience to the nascent hippie counterculture.
The popularization of entheogens by Wasson, Leary, authors Terence McKenna and Robert Anton Wilson, and others has led to an explosion in the use of psilocybin mushrooms throughout the world. By the early 1970s, many psilocybin mushroom species were described from temperate North America, Europe, and Asia and were widely collected. Books describing methods of cultivating Psilocybe cubensis in large quantities were also published. The availability of psilocybin mushrooms from wild and cultivated sources has made it among the most widely used of the psychedelic drugs.
At present, psilocybin mushroom use has been reported among some groups spanning from central Mexico to Oaxaca, including groups of Nahua, Mixtecs, Mixe, Mazatecs, Zapotecs, and others. An important figure of mushroom usage in Mexico was María Sabina.
Psilocybin is present in varying concentrations in about 200 species of Basidiomycota mushrooms. In a 2000 review on the worldwide distribution of psilocybin mushrooms, Gastón Guzmán and colleagues considered these to be distributed amongst the following genera: Psilocybe (116 species), Gymnopilus (14), Panaeolus (13), Copelandia (12), Hypholoma (6), Pluteus (6) Inocybe (6), Conocybe (4), Panaeolina (4), Gerronema (2), Agrocybe (1), Galerina (1) and Mycena (1). Guzmán increased his estimate of the number of psilocybin-containing Psilocybe to 144 species in a 2005 review.
The majority of these are found in Mexico (53 species), with the remainder distributed in the US and Canada (22), Europe (16), Asia (15), Africa (4), and Australia and associated islands (19). In general, psilocybin-containing species are dark-spored, gilled mushrooms that grow in meadows and woods of the subtropics and tropics, usually in soils rich in humus and plant debris. Psilocybin mushrooms occur on all continents, but the majority of species are found in subtropical humid forests. Psilocybe species commonly found in the tropics include P. cubensis and P. subcubensis. P. semilanceata—considered by Guzmán to be the world's most widely distributed psilocybin mushroom—is found in Europe, North America, Asia, South America, Australia and New Zealand, but is entirely absent from Mexico.
The effects of psilocybin mushrooms come from psilocybin and psilocin. When psilocybin is ingested, it is broken down to produce psilocin, which is responsible for the psychedelic effects. Psilocybin and psilocin create short-term increases in tolerance of users, thus making it difficult to abuse them because the more often they are taken within a short period of time, the weaker the resultant effects are. Psilocybin mushrooms have not been known to cause physical or psychological dependence (addiction).
Poisonous (sometimes lethal) wild-picked mushrooms can be mistaken for psilocybin mushrooms. Poisonous mushrooms can look very similar to certain psyilocybin containing mushrooms, and extreme care is advised when picking them outdoors.
As with many psychedelic substances, the effects of psychedelic mushrooms are subjective and can vary considerably among individual users. The mind-altering effects of psilocybin-containing mushrooms typically last from three to eight hours depending on dosage, preparation method, and personal metabolism. The first 3 - 4 hours of the trip are typically referred to as the 'peak' in which the user experiences more vivid visuals, and distortions in reality. However, the effects can seem to last much longer to the user because of psilocybin's ability to alter time perception.
In internet surveys, some psilocybin users have reported symptoms of hallucinogen persisting perception disorder, although this is uncommon and a causal connection with psilocybin use is unclear. There is a case report of perceptual disturbances and panic disorder beginning after using psilocybin mushrooms in frequent cannabis users with a pre-existing history of derealization and anxiety.
Magic mushrooms were rated as causing some of the least damage in the UK compared to other recreational drugs by experts in a study by the Independent Scientific Committee on Drugs. Other researchers have said that psilocybin is "remarkably non-toxic to the body's organ systems", explaining that the risks are indirect: higher dosages are more likely to cause fear and may result in dangerous behavior.
One study found the most desirable results may come from starting with very low doses first, and trying slightly higher doses over months. The researchers explain the peak experiences occur at quantities only slightly lower than a sort of anxiety threshold. Although risks of experiencing fear and anxiety increased somewhat consistently along with dosage and overall quality of experience, at dosages exceeding the individual's threshold, there was suddenly greater increases in anxiety than before. In other words, after finding the optimum dose, returns diminish for using more (since risks of anxiety now increase at a greater rate).
Noticeable changes to the auditory, visual, and tactile senses may become apparent around 30 minutes to an hour after ingestion, although effects may take up to two hours to take place. These shifts in perception visually include enhancement and contrasting of colors, strange light phenomena (such as auras or "halos" around light sources), increased visual acuity, surfaces that seem to ripple, shimmer, or breathe; complex open and closed eye visuals of form constants or images, objects that warp, morph, or change solid colours; a sense of melting into the environment, and trails behind moving objects. Sounds seem to be heard with increased clarity; music, for example, can often take on a profound sense of cadence and depth. Some users experience synesthesia, wherein they perceive, for example, a visualization of color upon hearing a particular sound.
As with other psychedelics such as LSD, the experience, or "trip", is strongly dependent upon set and setting. A negative environment could induce a bad trip, whereas a comfortable and familiar environment would allow for a pleasant experience. Many users find it preferable to ingest the mushrooms with friends, people with whom they are familiar, or people who are familiar with 'tripping'. Users have stated that you can control your trip by being in an environment or setting where they are unlikely to panic.
In 2006, the United States government funded a randomized and double-blinded study by Johns Hopkins University which studied the spiritual effects of psilocybin in particular. That is, they did not use mushrooms specifically (in fact, each individual mushroom piece can vary widely in psilocybin and psilocin content). The study involved 36 college-educated adults (average age of 46) who had never tried psilocybin nor had a history of drug use, and who had religious or spiritual interests. The participants were closely observed for eight-hour intervals in a laboratory while under the influence of psilocybin.
One-third of the participants reported the experience was the single most spiritually significant moment of their lives, and more than two-thirds reported it was among the top five most spiritually significant experiences. Two months after the study, 79% of the participants reported increased well-being or satisfaction; friends, relatives, and associates confirmed this. They also reported anxiety and depression symptoms to be decreased or completely gone. Fourteen months after the study, 64% of participants said they still experienced an increase in well-being or life satisfaction.
Despite highly controlled conditions to minimize adverse effects, 22% of subjects (8 of 36) had notable experiences of fear, some with paranoia, (The authors, however, reported that all these instances were "readily managed with reassurance.")
Advocates for advanced research in the field of ethnobotany have been asking for medical investigation of the use of synthetic and mushroom-derived psilocybin for the development of improved treatments of various neurological disorders, including chronic cluster headaches, following numerous anecdotal reports of benefits. There are also studies which include reports of psilocybin mushrooms sending both obsessive-compulsive disorders (OCD) and OCD-related clinical depression (both being widespread and debilitating mental health conditions) into complete remission immediately and for up to months at a time, compared to current medications which often have both limited efficacy and frequent undesirable side-effects. Recent studies done at Imperial College London and Johns Hopkins School of Medicine conclude, when used properly, psilocybin acts as an antidepressant as suggested by fMRI brain scans. The active components of psilocybin mushrooms have also been found to treat alcoholism and other addictions. The drugs potential as treatment to alcoholism is also similar to results found in relation to LSD in the 1950s and 60s. 
Dosage of mushrooms containing psilocybin depends on the potency of the mushroom (the total psilocybin and psilocin content of the mushrooms), which varies significantly both between species and within the same species, but is typically around 0.5–2.0% of the dried weight of the mushroom. A typical dose of the common species Psilocybe cubensis is about 1.0 to 2.5 g, while about 2.5 to 5.0 g dried mushroom material is considered a strong dose. Above 5 g is often considered a heavy dose.
The concentration of active psilocybin mushroom compounds varies not only from species to species, but also from mushroom to mushroom inside a given species, subspecies or variety. The same holds true even for different parts of the same mushroom. In the species Psilocybe samuiensis, the dried cap of the mushroom contains the most psilocybin at about 0.23%–0.90%. The mycelium contains about 0.24%–0.32%.
Psilocybin and psilocin are listed as Schedule I drugs under the United Nations 1971 Convention on Psychotropic Substances. Schedule I drugs are deemed to have a high potential for abuse and are not recognized for medical use. However, psilocybin mushrooms are not covered by UN drug treaties.
Psilocybin mushrooms are regulated or prohibited in many countries, often carrying severe legal penalties (for example, the US Psychotropic Substances Act, the UK Misuse of Drugs Act 1971 and Drugs Act 2005, and in Canada the Controlled Drugs and Substances Act).
Magic mushrooms in their fresh form still remain legal in some countries such as Austria. On November 29, 2008, the Netherlands announced it would ban the cultivation and use of psilocybin-containing fungi beginning December 1, 2008. The UK ban on fresh mushrooms (dried ones were illegal as they were considered a psilocybin-containing preparation) introduced in 2005 came under much criticism, but was rushed through at the end of the 2001-2005 Parliament; until then, magic mushrooms had been sold in the UK.
New Mexico appeals court ruled on June 14, 2005, that growing psilocybin mushrooms for personal consumption could not be considered "manufacturing a controlled substance" under state law. However it still remains illegal under federal law.