IMHO For the foreseeable future alcohol will always be a bigger threat to performance than controlled drugs. To focus on the lesser threat is a diversion, and in that sense I agree with Carnage.
My guess is that cocaine etc could become more of an issue over the next decade, as the demographic of increasing use that is documented in urban society generally moves it's way up through the age ladder and thus into responsible professions. Either that, or the typical 'user' will simply grow out of it and drug taking will remain orientated around a younger and more hedonistic mindset, but the social trends at the moment don't bear this out.
Right now though, my guess is it's statistically irrelevent. Sure it would make a great headline, but there's other more important stories to tell about issues in aviation safety.