A psychedelic substance is a psychoactive drug whose primary action is to alter cognition and perception. Psychedelics are part of a wider class of psychoactive drugs known as hallucinogens, a class that also includes related substances such as dissociatives and deliriants. Unlike other drugs such as stimulants and opioids which induce familiar states of consciousness, psychedelics tend to affect and explore the mind in ways that result in the experience being qualitatively different from those of ordinary consciousness. The psychedelic experience is often compared to non-ordinary forms of consciousness such as trance, meditation, yoga, and dreaming.
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The term psychedelic is derived from the Greek words ψυχή (psyche, "mind") and δηλείν (delein, "to manifest"), hence "mind-manifesting", the implication being that psychedelics can access and develop unused potentials of the human mind.[1] The word was coined in 1957 by British psychiatrist, Humphrey Osmond, loathed by American ethnobotanist, Richard Schultes, but championed by the American psychologist, Timothy Leary.[2]
Aldous Huxley had suggested to Humphrey Osmond in 1957 his own coinage phanerothymic (Greek "phanero-" visible + Greek "thymic" spiritual, thus "visible spirituality"). Recently, the term entheogenic has come into use to denote the use of psychedelic drugs in a positive and non-recreational context.
Psychedelic drugs act contrastingly according to substance on the processes of various serotonergic receptors, namely the 5-HT group and ligand gated ion channels. This action results in either excited or inhibited levels of cyclic adenosine monophosphate, inositol trisphosphate and diglyceride, neurochemicals responsible for a variety of biological functions. In the psychedelic experience, they affect a drastic cognitive and perceptual alteration and delineation of thought, accompanying all manner of hallucinations.
Psychedelics have a long history of traditional use in medicine and religion, where they are prized for their perceived ability to promote physical and mental healing. In this context, they are often known as entheogens. Native American practitioners using mescaline-containing cacti (most notably peyote, San Pedro, and Peruvian Torch) have reported success against alcoholism, and Mazatec practitioners routinely use psilocybin mushrooms for divination and healing. Ayahuasca, which contains the powerful psychedelic DMT, is used in Peru and other parts of South America for spiritual and physical healing as well as in religious festivals.
'Classic' or serotonergic psychedelics (agonists for the 5-HT2A serotonin receptors) include LSD, psilocybin (the active constituent of psilocybin mushrooms, commonly known as "magic mushrooms"), mescaline (the active constituent of Peyote), and DMT (the active constituent of Ayahuasca and potentially an endogenous psychedelic compound). A few newer synthetics such as MDMA and 2C-B have also enjoyed some popularity. Cannabis, one of the most widely used psychoactive drugs in the world, produces effects similar to low doses of classic psychedelics, though at higher doses or in susceptible individuals it can be quite psychedelic, depending on the strain.
This class of psychedelics includes the classical hallucinogens, including the ergolines like LSD and LSA, tryptamine-based compounds like psilocybin and DMT, and phenethylamine-based compounds like mescaline and 2C-B. Many of the tryptamines and phenethylamines cause remarkably similar effects, despite their different chemical structure. However, most users report that the two families have subjectively different qualities in the "feel" of the experience, which are difficult to describe. At lower doses, these include sensory alterations, such as the warping of surfaces, shape suggestibility, and color variations. Users often report intense colors that they have not previously experienced, and repetitive geometric shapes are common. Higher doses often cause intense and fundamental alterations of sensory perception, such as synesthesia or the experience of additional spatial or temporal dimensions. Some compounds, such as 2C-B, have extremely tight "dose curves", meaning the difference between a non-event and an overwhelming disconnection from reality can be very slight. There can be very substantial differences between the drugs, however. For instance, 5-MeO-DMT rarely produces the visual effects typical of other psychedelics and ibogaine (a 'complex tryptamine') is also an NMDA receptor antagonist and κ-opioid receptor agonist in addition to being an agonist for the 5-HT2A receptors, resulting in dissociative effects as well (see dissociatives below).
The empathogen-entactogens are phenethylamines of the MDxx class such as MDMA, MDEA, and MDA. Their effects are characterized by feelings of openness, euphoria, empathy, love, heightened self-awareness, and by mild audio and visual distortions (an overall enhancement of sensory experience is often reported). Their adoption by the rave subculture is probably due to the enhancement of the overall social and musical experience. MDA is atypical to this experience, often causing hallucinations and psychedelic effects in equal profundity to the chemicals in the 5-HT2A agonist category , but with substantially less mental involvement, and is possibly both a serotonin releaser and 5-HT2A receptor agonist.
The cannabinoid tetrahydrocannabinol (THC) and related compounds are capable of activating the brain's endocannabinoid system. Some effects may include a general change in consciousness, mild euphoria, feelings of general well-being, relaxation or stress reduction, enhanced recollection of episodic memory, hunger, increased sensuality, increased awareness of sensation, creative or philosophical thinking, disruption of linear memory, paranoia, agitation, and anxiety, potentiation of other psychedelics, and increased awareness of sound, patterns and color. They are more similar to the above categories as dose increases.
Certain dissociative drugs acting via NMDA antagonism are known to produce what some might consider psychedelic effects. The main differences between dissociative psychedelics and serotonergic hallucinogens are that the dissociatives cause more intense derealization and depersonalization.[3] For example, ketamine produces sensations of being disconnected from one's body and that the surrounding environment is unreal, as well as perceptual alterations seen with other psychedelics.[4] Because the effects of dissociatives tend to add a far more sedating and sensory deprived quality to the experience, they are often not considered true psychedelics.
Salvia divinorum is a dissociative that is sometimes classified as an atypical psychedelic. The active molecule in the plant, Salvinorin A, is a kappa opioid receptor agonist, working on a part of the brain that deals with pain. Activation of this receptor is also linked to the dysphoria sometimes experienced by users of opiates either therapeutically or recreationally. This explains, to an extent, the majority of S. divinorum experiences which are reported as negative. An unusual feature of S. divinorum is its high potency (dosage is in the microgram range) and extremely disorienting effects, which often include "entity contact", complete loss of reality-perception and user's experiencing their consciousness as being housed in different objects i.e. a pane of glass or a pencil. It is also unusual as it is a terpenoid like THC as opposed to an alkaloid like the comparably intense serotonergic psychedelics and NMDA receptor antagonists mentioned above.
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