Amid an opioid epidemic, the rise of deadly synthetic drugs and the widening legalization of marijuana, a curious bright spot has emerged in the youth drug culture: American teenagers are growing less likely to try or regularly use drugs, including alcohol.

With minor fits and starts, the trend has been building for a decade, with no clear understanding as to why. Some experts theorize that falling cigarette-smoking rates are cutting into a key gateway to drugs, or that antidrug education campaigns, long a largely failed enterprise, have finally taken hold.