1.NounAn antihistamine and anticholinergic drug that blocks the effect of histamine at H1 receptor sites, relieving allergy symptoms. It also reduces smooth muscle contraction, increases heart rate, and sedates the user by blocking muscarinic acetylcholine receptors (mAChRs).
"Diphenhydramine is a convenient and cheap antihistamine for use, but there are other drugs that do not make the user tired."