4-HO-DET is a novel substituted tryptamine closely related to Psilocin and Psilocybin. It was invented in the 1950s by Albert Hofmann and Franz Troxler in the Sandoz lab under the lab code CZ-74. Together with its phosphoric acid ester 4-PO-DET (CEY-19), it was provided to German research scientists for testing and evaluation. (Leuner & Baer 1965). 4-HO-DET is also referred to as 4-Hydroxy-N, N –diethyltryptamine.
4-HO-DET belongs in a category called 4-substituted tryptamines, the classics of which include Psilocybin and Psilocin. Many such substitutions in this pattern have been developed, some of which have been studied and tested in various degrees.
A series of studies were conducted and published in the 1960s by Dr. Hanscarl Leuner and G. Baer, involving clinical trials with human volunteers (Leuner & Baer 1965; Baer 1967; Leuner 1962). The trials were done with a range of dosages. The established physical effects noticed, included slight increases in pulse rate, body temperature, and blood pressure, nausea, hypersalivation, mydriasis (dilation of pupils), somewhat increased reflexes, and disturbances in coordination.
Rarely and only with the highest dosages used, were neurotic symptoms noticed. These included delirium, depersonalization, and paranoia (Baer 1967).
With respect to duration, 4-HO-DET exhibited a reduced duration of activity. It is characterized as being relatively abrupt in its comedown and duration, with less psychological side effects in comparison with psilocybin.
In the late 1980s, Jochen Gartz, a colleague of the late Alexander Shulgin, discovered a novel means of synthesis of 4-PO-DET. P. Cubensis mushrooms were grown from a mycelia substrate supplemented with N,N – Diethyltryptamine (DET) HCl. Both 4-PO-DET and 4-HO-DET were isolated from the mushroom and confirmed using HNMR or LC-MS analysis. 
In addition, it was found that the mushrooms yielded up to 3.3% alkaloid content by dried weight (whereas on average, the typical magic mushroom only contains 1-2% psilocin/psilocybin by dried weight). The ideal saturation was found to be 0.25 mmol per 13.5 grams of mycelial substrate. Spores for Psilocybe cubensis were inoculated into the substrate.
The concept works as a result of the metabolism of the mushroom. Psilocybin, the active tryptamine found in Psilocybe cubensis, is a metabolite of tryptophan.  This means that the mushroom takes tryptophan from its food source, and metabolizes it into psilocybin (in the same way that the human body uses tryptophan to produce serotonin). The idea works thusly: the enzymes that convert tryptophan into psilocybin can also convert other tryptamines into psilocybin analogs. If DMT is supplemented into the food source of the mushroom, it will metabolize it into psilocybin (because DMT is a metabolic intermediate between tryptophan and psilocybin). If, however, a synthetic DMT analog is supplemented into the food source–such as, for example, DET (N,N-diethyltryptamine), the same enzymes that produce psilocybin will instead produce ethocybin (4-PO-DET) and ethocin (4-HO-DET). This is because the enzymes recognize any indole compound and are not selective or discriminatory about what metabolites they produce. This is described in the book TIHKAL by Alexander Shulgin:
“Some fascinating studies have been done in Germany where the metabolically active mycelium of some Psilocybe species have been administered diethyltryptamine as a potential diet component. Normally, this mushroom species dutifully converts N,N-dimethyltryptamine (DMT) to psilocin, by introducing a 4-hydroxyl group into the molecule by something that is probably called an indole 4-hydroxylase by the biochemists. You put DMT in, and you get 4-hydroxy-DMT out, and this is psilocin. Maybe if you put Mickey Mouse in, you would get 4-hydroxy-Mickey Mouse out. It is as if the mushroom psyche didn’t really care what it was working with, it was simply compelled to do its sacred duty to 4-hydroxylate any tryptamine it came across. It was observed that if you put N,N-diethyltryptamine (DET, not a material found in nature) into the growing process, the dutiful and ignorant enzymes would hydroxylate it to 4-hydroxy-N,N-diethyltryptamine (4-HO-DET) a potent drug also not known in nature. This is the title drug of this commentary. What a beautiful burr to thrust into the natural versus synthetic controversy. If a plant (a mushroom mycelium in this case) is given a man-made chemical, and this plant converts it, using its natural capabilities, into a product that had never before been known in nature, is that product natural? What is natural? This is the stuff of many long and pointless essays.”
Gartz conducted further research by adding NMT (N-methyl-Tryptamine) to the substrate and found that it yielded mushrooms with exclusively 4-HO-NMT (4-hydroxy-N-methyltryptamine) and Baeocystin (4-PO-NMT, 4-phoshporyloxy-N-methyltryptamine).
Additionally, adding DPT (N,N–Dipropyltryptamine) to the substrate, yielded mushrooms with 4-HO-DPT/4-PO-DPT, whilst adding DiPT (N,N-Diisopropyltryptamine) to the substrate, yielded mushrooms with 4-HO-DiPT/4-PO-DiPT .
In 2021, further research from another group found that adding 5-methyl-DMT (a synthetic DMT analog) into the growing substrate of Psilocybe cubensis resulted in mushrooms which contained 5-methylpsilocin (4-HO-5-Me-DMT), instead of regular psilocybin . This is because the same enzymes, which would normally metabolize tryptophan into psilocybin, instead metabolized 5-Me-DMT into 4-HO-5-Me-DMT. This further confirms the theory of bioconversion, and provides strong evidence that the enzymes responsible for the biosynthesis of psilocin/psilocybin can recognize a potentially wide variety of tryptamines as enzymatic substrate, including synthetic tryptamines, and produce biosynthetic psilocin analogs as metabolites.
The fundamental route of metabolism typically being:
Tryptophan -> Tryptamine -> NMT/DMT -> 4-HO-NMT/psilocin- > baeocystin/psilocybin