Adderall and the other stimulants will probably improve the concentration of most people who take them.  This has led to their popularity as "study drugs" on college campuses.  Similar amphetamines have been used in the military to help soldiers and pilots stay alert during combat missions.  Truck drivers have been known to take them to stay awake on long hauls.

These drugs can have severe side-effects, however.  Amphetamines and related drugs can cause dependence and addiction, and higher doses are sometimes needed over time to achieve the same effect (tolerance).   Some amphetamine relatives such as phentermine are used as diet pills.