I'm not sure you could get in trouble for something like caffeine pills, since you wouldn't get in trouble for having the same amount of caffeine in Coke form, but who knows...people who run schools can be dicks. Yes, you can just buy them at any drug store without getting carded. There's no difference, legally speaking, between caffeine pills and caffeine in beverage form (at least in the USA). I wouldn't expect to make too much of a profit off of them though if you're planning on selling them, since anybody can just buy them from a store.