Various drugs hamper the ability of the subconscious to determine whether a person is able to will magic or not. Hence, the use of such drugs is a way to overcome limitations and to cast magic even if they’ve already failed and are otherwise impotent. Of course, drug-induced potency only lasts for as long as they’re under the drug’s influence; once they have recovered, they are back to being impotent. Experience willing magic has no impact on then whey’re not under the effect. Also, drug use results in the development of drug tolerance, so that one has to use steadily increasing amounts of the drug to remain potent. Also, since these drugs by necessity have to hamper judgment capability, this is not a true replacement for true potential. Doping can be considered a form of situational requirement.
Over time, various herbs and concoctions that may first not have any effect but which are believed to have these effects, will actually come to have them, as more and more people believe that those herbs and concoctions have drug properties.