Binding selectivity in the context of Pharmacology of selegiline

Psilocybin, also known as 4-phosphoryloxy-N,N-dimethyltryptamine (4-PO-DMT), is a naturally occurring tryptamine alkaloid and investigational drug found in more than 200 species of mushrooms, with hallucinogenic and serotonergic effects. Effects include euphoria, changes in perception, a distorted sense of time (via brain desynchronization), and perceived spiritual experiences. It can also cause adverse reactions such as nausea and panic attacks.

Psilocybin is a prodrug of psilocin. That is, the compound itself is biologically inactive but quickly converted by the body to psilocin. Psilocybin is transformed into psilocin by dephosphorylation mediated via phosphatase enzymes. Psilocin is chemically related to the neurotransmitter serotonin and acts as a non-selective agonist of the serotonin receptors. Activation of one serotonin receptor, the serotonin 5-HT_2A receptor, is specifically responsible for the hallucinogenic effects of psilocin and other serotonergic psychedelics. Psilocybin is usually taken orally. By this route, its onset is about 20 to 50 minutes, peak effects occur after about 1 to 2 hours, and its duration is about 4 to 6 hours.

JWH-018 (1-pentyl-3-(1-naphthoyl)indole, NA-PIMO or AM-678) is an analgesic chemical from the naphthoylindole family that acts as a full agonist at both the CB₁ and CB₂ cannabinoid receptors, with some selectivity for CB₂. It produces effects in animals similar to those of tetrahydrocannabinol (THC), a cannabinoid naturally present in cannabis, leading to its use as synthetic cannabinoid products that, in some countries, are sold legally as "incense blends".

As a full agonist at both the CB₁ and CB₂ cannabinoid receptors, this chemical compound is classified as an analgesic medication. The analgesic effects of cannabinoid ligands, mediated by CB₁ receptors are well established in treatment of neuropathic pain, as well as cancer pain and arthritis.

Gaboxadol, also known as 4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol (THIP) and by its former developmental code names Lu-2-030, MK-0928, and OV101, is a GABA_A receptor agonist related to muscimol which was investigated for the treatment of insomnia and other conditions like Angelman syndrome but was never marketed. At lower doses, the drug has sedative and hypnotic effects, and at higher doses, it produces hallucinogenic effects. It is taken orally.

The drug acts as a potent and selective partial agonist of the GABA_A receptor, the major signaling receptor of the inhibitory endogenous neurotransmitter γ-aminobutyric acid (GABA). However, it acts as a preferential supra-maximal agonist at extrasynaptic δ subunit-containing GABA_A receptors. In contrast to GABA_A receptor positive allosteric modulators like benzodiazepines and Z drugs, gaboxadol is an orthosteric agonist of the GABA_A receptor, acting on the same site as GABA rather than at an allosteric regulatory site. As a result, gaboxadol has differing effects from benzodiazepines and related drugs. Gaboxadol is a conformationally constrained synthetic analogue of GABA and of muscimol, an alkaloid and hallucinogen found in Amanita muscaria (fly agaric) mushrooms. It has greatly improved drug-like properties compared to these compounds.

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.

A lead compound (/ˈliːd/, i.e., a "leading" compound; not to be confused with various compounds of the element lead) in drug discovery is a chemical compound that has pharma­co­logical or biological activity likely to be therapeutically useful, but may never­the­less have suboptimal structure that requires modification to fit better to the target; lead drugs offer the prospect of being followed by "back-up" compounds. The chemical structure serves as a starting point for chemical modifications in order to improve potency, selectivity, or pharma­co­kinetic parameters. Furthermore, newly-invented pharma­co­logically active moieties may have poor druglikeness and may require chemical modification to become "drug-like" enough to be tested biologically or clinically.

Lead compounds are sometimes called developmental candidates. This is because the discovery and selection of lead compounds occurs prior to preclinical and clinical development of the candidate.