You can responsibly use amphetamine or modafinil without serious side effects. Amphetamine enhances the mental performance of millions of our children and few people seem to be complaining about long term side effects.

The military has studied the use of amphetamine and modafinil in extreme situations. If you go without sleep for three days, there's going to be serious side effects, with or without any drug. I doubt that any of the scientists on stimulants are using it that extremely, which means the side effects are limited.