Stimulants do improve athletic performance; there is ample evidence for this. Back when I was a swimmer (Pac-10 college), we were routinely drug tested for stimulants, including methylphenidate and dextroamphetamine. Regardless of prescription, they are illegal in top-level swimming. Most of the guys I swam with (and I) just got all hopped up on coffee instead. That said, an endurance/aerobic sport like swimming is fundamentally different from pitching. Certainly it's useful if you get tired after 110 pitches instead of 90 pitches, but while swimming is a game of hundredths of seconds, pitching is a game of hundredths of inches. Command, control, placement, whatever you want to call it, it's more important than aerobic endurance. I actually wonder what kind of advantage a pitcher would get out of it. I'm not sure it'd be much. And while I don't think it beyond the pale to think a pitcher would take it for performance reasons, I'm not ready to draw any conclusions about Gray's use, or even to conclude that it hurts his draft stock.