Benadryl is a brand name for a number of different antihistamine medications used to stop allergies. In the United States and Canada, it is the first-generation antihistamine diphenhydramine. Benadryl for Cats: Although cats can take Benadryl, it has potential side effects, including hyperexcitability, diarrhea, decreased appetite and urination, dry mouth, vomiting and sedation. Benadryl can react with a variety of drugs; Drowsiness is a side effect of taking Benadryl for cats just as it is for humans.. Many dogs are given Benadryl to help them fend off allergic reactions. But can you give a cat Benadryl? Veterinarians weigh in on whether Benadryl is safe for cats. Benadryl is a common OTC medication used by humans to treat a variety of illnesses, but not many people are aware of its effectiveness in the treatment of household pets including dogs. Benadryl, also known by its generic name diphenhydramine, is one of the few over-the-counter drugs that veterinarians routinely have owners administer at home. While it is generally well tolerated and has a wide safety margin, there are a few things owners should keep in mind before dosing it at What is the liquid benadryl dosaging for cats. My vet gave me a dosaging a couple of years ago for long distance travelling and I did not save it. It sure did h FINDING THE CORRECT BENADRYL DOSAGE FOR DOGS. The usual dose of Benadryl for dogs (adult) is 2 to 4 milligrams per kilogram of body weight, which corresponds to a dose of 0.9 to 1.8 miligrams per pound of body weight, according to the Merck Veterinary Manual. On Jan 28, 2007. Thanks Chanda4, but Benadryl knocks me out and I need to find something I can take when I'm traveling - or driving - that won't make me drowsy. What is Diphenhydramine (Generic Benadryl)? Diphenhydramine is an antihistamine used to relieve allergy symptoms, insect stings, motion sickness, travel anxiety, and other conditions. Find patient medical information for Benadryl Oral on WebMD including its uses, side effects and safety, interactions, pictures, warnings and user ratings.