I would discourage the use of amphetamines without a real mental need, they do have some very serious side effects. However I have found due to a combination of mental disorders - mostly depression related - I am unable to function without amphetamines during certain times of the month.

As an alternative to stronger amphetamines I have found provigil - http://en.wikipedia.org/wiki/Modafinil - to be a wonder drug. It doesn't stay in the body as long, yet gives you enough umph to get going on those real tough days.