(Warning:I am not a doctor,and you must fully understand the side effects before using even a mild amphetamine)
Here is a very good quora thread on the long term effects http://www.quora.com/What-are-the-long-term-effects-of-Adder...
Also nearly 3.3 million Americans age 19 and younger used an ADHD drug last year, according to Medco Health Solutions Inc.I think there is enough data to conclude that there are not really any serious and irreversible long term effects.Would love to be proved wrong on this?
"After 1971 he also took amphetamines, despite the concern of his friends, one of whom (Ron Graham) bet him $500 that he could not stop taking the drug for a month.[12] Erdős won the bet, but complained that during his abstinence mathematics had been set back by a month: "Before, when I looked at a piece of blank paper my mind was filled with ideas. Now all I see is a blank piece of paper." After he won the bet, he promptly resumed his amphetamine use."