 The main disadvantage of THC phosphate ester is the slow rate of hydrolysis of the ester link, resulting in delayed onset of action and lower potency than the parent drug.Pharmacologically, it parallels the action of psilocybin as a metabolic prodrug for psilocin.THC phosphate ester is made by reacting THC with phosphoryl chloride using pyridine as a solvent, following by quenching with water to produce THC phosphate ester.