Each Benadryl tablet and liquid-filled capsule contains 25 milligrams (mg) of diphenhydramine. Children’s Benadryl liquid has 12.5 mg per teaspoon. We suss out the safest – and the most sneeze-inducing – cats for allergy-prone people. 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 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.. 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 When allergies or anxiety takes over your pet, you know how hard it is to watch them go through that pain. However, there is a solution: Benadryl for dogs. Find patient medical information for Benadryl Oral on WebMD including its uses, side effects and safety, interactions, pictures, warnings and user ratings. Kid-friendly antihistamine allergy relief in an easy-to-take chewable tablet. BENADRYL® Chewables help your child feel better when they need it most. Learn more. Allergens are more prominent at different times of year. Our Allergy Calendar will help you find out the common seasons for different allergies in the UK. Benadryl at Walgreens. View current promotions and reviews of Benadryl and get free shipping at $35.