Diphenhydramine HCL ("benadryl") is a sleeping medicine. It's the active ingredient in many sleep aids, such as Tylenol Simply Sleep, and is often sold and used specifically for that purpose. In fact, if he were to buy an over-the-counter pill instead of benadryl, he'd probably be taking the exact same medicine in the exact same dosage (just under a different name brand).
The only difference is that the benadryl company markets it as an antihistamine, but it's still the exact same medicine.
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