Norbaeocystin, also known as 4-phosphoryloxytryptamine (4-PO-T), is a psilocybin mushroom alkaloid of the tryptamine family and an analogue of psilocybin (4-PO-DMT). It is found as a minor compound in most psilocybin mushrooms, together with psilocybin, psilocin (4-HO-DMT), aeruginascin (4-PO-TMT), and baeocystin (4-PO-NMT), from which it is a derivative.
Norbaeocystin is generally thought to be non-psychoactive, although this has not been confirmed.
Norbaeocystin (4-PO-T) is thought to be a prodrug of 4-hydroxytryptamine (4-HT), analogously to how psilocybin (4-PO-DMT) is a prodrug of psilocin (4-HO-DMT) and baeocystin (4-PO-NMT) is thought to be a prodrug of norpsilocin (4-HO-NMT). 4-HT is a potent and centrally penetrant serotonin 5-HT<sub>2A</sub> receptor agonist and also interacts with other serotonin receptors. In spite of this however, 4-HT and norbaeocystin do not produce the head-twitch response, a behavioral proxy of psychedelic effects, in animals, and hence are putatively non-hallucinogenic. The reasons for this are unknown, but may be due to ò-arrestin2-preferring biased agonism of the serotonin 5-HT<sub>2A</sub> receptor.
Norbaeocystin is an N-demethylated derivative of baeocystin (itself an N-demethylated derivative of psilocybin), and a phosphorylated derivative of 4-hydroxytryptamine (4-HT). The latter is notable as a positional isomer of serotonin, which is 5-hydroxytryptamine (5-HT).
Derivatives of norbaeocystin (4-PO-T), also known as substituted 4-phosphoryloxytryptamines, include baeocystin (4-PO-NMT), psilocybin (4-PO-DMT), ethocybin (4-PO-DET), 4-PO-DiPT, 4-PO-MET, and aeruginascin (4-PO-TMT), among others.
Norbaeocystin was found to be sold as an analytical standard in 2023.