Meh. Unless you're a fighter pilot or your ability to stay awake/concentrate is a matter of life and death, any benefits are outweighed by the risks of dependence and abuse.
Adult ADHD is WAY overdiagnosed and overprescribed for, as are most other medical/psychological "conditions"). Only difference is that the stimulants used to treat it have a huge potential for dependence and recreational abuse. The abuse of this stuff is truly becoming an epidemic, as was pointed out in the article somebody else linked to.
I know that in baseball, there are tons of players that quickly got diagonses of ADHD the second that greenies were put on the banned substance list. If the NFL has the same policy of allowing players to use Ritalin etc. if they have a valid presciption, then it means that Spikes obviously did not and had another big lapse in judgment. This scenario matches up perfectly with what Spikes said publicly, so it's a pretty fair bet that he was using recreationally.
Lesson learned hopefully, and he's ready to kick some butt in the playoffs.