Diphenhydramine (Benadryl): Toxic or Terrific? More commonly known by its brand name Benadryl, Diphenhydramine is a household name and a staple of almost every medicine cabinet. Used for everything from colds and flu to hives, Benadryl has a broad application and is widely available. Those with seasonal allergies are probably familiar with pharmaceutical medications like Allegra, Claritin, and Zyrtec for dealing with those pesky allergic reactions like watery and itchy eyes, nasal congestion, and an overall sense of being run down and depleted. Most often called on as an antihistamine to calm the body’s natural inflammatory response, Benadryl does so somewhat reliably, but not without impacting the body with a range of undesirable side effects.