Speed makes me paranoia and stressed and has it some really nasty side effects. I have seen people take it too much too often and that didn't look healthy to me - to use an understatement.
They might use amphetamins or derivatives as medicines, but still the addictive property of this substance seems dangerous to me.
But like everything it is always a matter of moderation, it won't do much harm in a low dossage used once in a while. I will stick to some red bull, ephedra, caffeine or X to get in a party mood...