Even if he was taking Adderall last year it wouldn't explain his sudden success (at least not by itself) because he'd been using it under a medical exemption through the early years of his career. Baseball has reportedly been cutting back on those exemption ones because a ridiculously high percentage of players getting one (about 1 in 6 were claiming to have ADD so they could take it). The testing also requires two failures to get a suspension. MLB hasn't announced when he failed the first time. It could have been in 2013.