I'm no clubhouse lawyer but I believe that Adderall (Dextroamphetamine/Amphetamine) is OK by the NFL if you have prescription. Why the fuck don't the players just get a prescription? And based upon my limited knowledge, I don't think Petey is treating his ADD/ADHD with meds.
They probably aren't actually getting caught for Adderall. The NFL does not make the substances known when a player is caught. They just release a statement saying player x has violated the NFL drug policy. The Adderall stuff came from the players, not the league.