Benadroxine (the drug used on the murder victims) is a fictional antihistamine. Its name appears to be a combo of two commonly used antihistamines: Benadryl (Diphenhydramine), an over the counter antihistamine mainly used to treat seasonal allergies and minor insomnia; and hydroxyzine (Atarax), a prescription antihistamine used to treat itching, anxiety, nausea and motion sickness.