'plain' fentanyl was measured to have an IC50 of 1.14 nM.
4'-methoxy fentanyl had an IC50 of 810 nM.
4'-hydroxy fentanyl has an IC50 of 86 nM.
so if the same relationship holds true, 4-meo-butyrfentanyl should be 100x less potent than its parent. its metabolite should be 10x less.
That's...