QUESTION & ANSWER
Why does Benadryl make you sleepy?
Benadryl (diphenhydramine) blocks the chemical histamine. Histamine is involved in causing allergy and cold symptoms. It also plays a role in wakefulness. When Benadryl blocks histamine, it takes away its stimulation of wakefulness. Many people experience this as drowsiness and can use Benadryl to sleep.