Final answer:
Diphenhydramine (Benadryl) can produce additive effects when given concomitantly with alprazolam (Xanax).
Step-by-step explanation:
When reviewing the client's medication history before administering alprazolam (Xanax), the nurse should be aware that Diphenhydramine (Benadryl) can produce additive effects when given concomitantly with alprazolam. This means that taking diphenhydramine and alprazolam together can enhance the effects of both drugs, potentially leading to increased sedation and central nervous system depression.