My bro mixes Adderall (dextroamphetamine and racemic amphetamine) 40mg & lortab 7.5mg. I'm scared about how that combo may hurt his health. What reactions can it cause him to experience? :/

Depends. Lortab has a sedative effect while Adderall (dextroamphetamine and racemic amphetamine) has an excitarory effect. In addition, the medical literature indicates that Adderall (dextroamphetamine and racemic amphetamine) potentates the effects of lortab. If one physician has prescribed both medications he/she may have a reason for mixing the two. In any case, all of your brother's physicians should know all of the medications he is taking.