5-HT2A receptor in the context of "Psilocybin"

Hallucinogens, also known as psychedelics, entheogens, or historically as psychotomimetics, are a large and diverse class of psychoactive drugs that can produce altered states of consciousness characterized by major alterations in thought, mood, and perception as well as other changes. Hallucinogens are often categorized as either being psychedelics, dissociatives, or deliriants, but not all hallucinogens fall into these three classes.

Examples of hallucinogens include psychedelics or serotonin 5-HT_2A receptor agonists like LSD, psilocybin, mescaline, and DMT; dissociatives or NMDA receptor antagonists like ketamine, PCP, DXM, and nitrous oxide; deliriants or antimuscarinics like scopolamine and diphenhydramine; cannabinoids or cannabinoid CB₁ receptor agonists like THC, nabilone, and JWH-018; κ-opioid receptor agonists like salvinorin A and pentazocine; GABA_A receptor agonists like muscimol and gaboxadol; oneirogens like ibogaine and harmaline; and others like nutmeg, carbogen, glaucine, and hallucinogenic bolete mushrooms.

Lysergic acid diethylamide, commonly known as LSD (from German Lysergsäurediethylamid) and by the slang names acid and lucy, is a semisynthetic hallucinogenic drug derived from ergot, known for its powerful psychological effects and serotonergic activity. It was historically used in psychiatry and 1960s counterculture; it is currently legally restricted but experiencing renewed scientific interest and increasing use.

When taken orally, LSD has an onset of action within 0.4 to 1.0 hours (range: 0.1–1.8 hours) and a duration of effect lasting 7 to 12 hours (range: 4–22 hours). It is commonly administered via tabs of blotter paper. LSD is extremely potent, with noticeable effects at doses as low as 20 micrograms and is sometimes taken in much smaller amounts for microdosing. Despite widespread use, no fatal human overdoses have been documented. LSD is mainly used recreationally or for spiritual purposes. LSD can cause mystical experiences. LSD exerts its effects primarily through high-affinity binding to several serotonin receptors, especially 5-HT_2A, and to a lesser extent dopaminergic and adrenergic receptors. LSD reduces oscillatory power in the brain's default mode network and flattens brain hierarchy. At higher doses, it can induce visual and auditory hallucinations, ego dissolution, and anxiety. LSD use can cause adverse psychological effects such as paranoia and delusions and may lead to persistent visual disturbances known as hallucinogen persisting perception disorder (HPPD).

An oneirogen, from the Greek ὄνειρος óneiros meaning "dream" and gen "to create", is a substance that induces a dream-like state of consciousness. Oneirogens function by altering neural processing in a way that shifts the brain from bottom-up sensory input to top-down generative activity, resembling the mechanisms involved in dreaming. This neural shift is associated with increased internal imagery and reduced responsiveness to external stimuli. Psychedelics—particularly those acting on the 5-HT2A receptor—produce oneirogenic effects by promoting this altered balance of neural signaling.

Glaucine (also known as 1,2,9,10-tetramethoxyaporphine, bromcholitin, glauvent, tusidil, and tussiglaucin) is an aporphine alkaloid found in several different plant species in the family Papaveraceae, such as Glaucium flavum, Glaucium oxylobum, and Corydalis yanhusuo, and in other plants such as Croton lechleri in the family Euphorbiaceae.

It has bronchodilator, neuroleptic and antiinflammatory effects, acting as a PDE4 inhibitor and calcium channel blocker, and is used medically as an antitussive in some countries. TLRs plays role in its anti inflammatory effects. Glaucine may produce side effects such as sedation, fatigue, and a hallucinogenic effect characterised by colourful visual images, and has been detected as a novel psychoactive drug. In a 2019 publication, the isomer (R)-glaucine is reported to be a positive allosteric modulator of the 5-HT2A receptor, which is also associated with the hallucinogenic effects of substances such as psilocybin and mescaline.

Ketanserin, sold under the brand name Sufrexal, is an antihypertensive agent which is used to treat arterial hypertension and vasospastic disorders. It is also used in scientific research as an antiserotonergic agent in the study of the serotonin system; specifically, the 5-HT₂ receptor family. The drug is taken by mouth.

Side effects of ketanserin include dizziness, tiredness, edema, dry mouth, weight gain, and QT interval prolongation. Ketanserin acts as a selective antagonist of the serotonin 5-HT_2A, α₁-adrenergic, and histamine H₁ receptors. It also shows lower affinity for various other targets.

Psilocin, also known as 4-hydroxy-N,N-dimethyltryptamine (4-HO-DMT), is a psychedelic drug and fungal alkaloid of the tryptamine and 4-hydroxytryptamine families. Along with its phosphate ester psilocybin, it is found in most species of psilocybin-containing mushrooms, such as Psilocybe cubensis and Psilocybe mexicana, and is the compound responsible for their hallucinogenic effects, although concentrations of psilocin are variably lower than those of psilocybin. The drug is taken orally and its effects include perceptual changes and visual effects, emotional changes, ego dissolution, time dilation, and mystical experiences, among others. Psilocybin, as well as synthetic acyl esters such as 4-AcO-DMT (psilacetin; O-acetylpsilocin) and 4-PrO-DMT (O-propionylpsilocin), are prodrugs of psilocin and have similar properties and effects.

Psilocin acts as a non-selective serotonin receptor agonist, including of the serotonin 5-HT_2A receptor among others. The drug produces its hallucinogenic effects specifically via activation of the serotonin 5-HT_2A receptor. However, other serotonin receptors, such as the serotonin 5-HT_1A and 5-HT_2C receptors, may also contribute to its effects. Notable analogues of psilocin include dimethyltryptamine (DMT), its positional isomer bufotenin (5-HO-DMT), its higher homologue 4-HO-MET (metocin), and others.