Adderall is often prescribed to people with Attention Deficit Hyperactivity Disorder in order to increase their ability to concentrate. Since it is made up of amphetamines, it often produces a "speedy" effect as well.
Nicole has denied having an eating disorder on numerous occasions, but she allegedly likes that Adderall has a special side effect: appetite suppression. Says an insider, "[Nicole] loves Adderall because she stays awake, and it makes her not want to eat. And she takes it even more when she's filming."