Subject: Amphetamine, a stimulant, was used to treat hyperactivity?

I came across the use of amphetamine when read about narcolepxy. It is used 
to keep narcoleptic awake by manipulating the receptor-hormone interaction. 
Yet, i found that it is also used to treat attention deficit hyperactivity. 
And also, i was found that this is done by helping those hyperactive to be 
able to concentrate. It seems to me that the latter effect is somehow 
contradict with the previous one. I am curious of knowing the mechanism 
behind it. thanks...

Re: Amphetamine, a stimulant, was used to treat hyperactivity?