There will always be substance users. There will always be substance abusers. The former may be seeking ideas or insight or temporary intoxication (ever see kids spin around till they're so dizzy they fall down?) or escape; the latter may be trying to duck from unpleasant, boring or painful circumstance.
Drug use isn't some monolithic cause/effect machine. And culture-embedded drug use has been around for thousands of years.
I suppose there is a baseline that will always be there, there are always seekers, the curious and the addicted. That it is higher in the US will be due to reasons beyond the baseline, and are likely to be related to the way drugs are mystified and not dealt with honestly (just as the teen pregnancy and STD issues the US sees are likely related to the way sex is mystified and not dealt with honestly).
Socially, the US does have extremes of pampering versus want. These extremes most likely produce boredom and hopelessness, which must feed into the bigger picture.