Diphenhydramine (Benadryl) Diphenhydramine hydrochloride is a chemical mainly used as an antihistamine, antiemetic, sedative, and hypnotic. It is produced and marketed under the trade name Benadryl by McNeil-PPC (a division of Johnson & Johnson) in the U.S. & Canada, and Dimedrol in other countries. It is also found in the name-brand products Nytol and Unisom, though some Unisom products contain doxylamine instead. The observed effects of having consumed diphenhydramine may result in marked sedation, including drowsiness, reduced wakefulness, altered mood, impaired cognitive and psychomotor performance. In the DUI context relating to field sobriety testing, horizontal gaze nystagmus, vertical gaze nystagmus (at high doses), and lack of convergence are present. Pupil size is normal, dilatation may occur and reaction to light is slow. Pulse rate, blood pressure, and body temperature are normal. Id.