Benadryl is an antihistamine medication used for allergies in humans. It is also safe to give to dogs and cats who have allergies. It is important to know that Benadryl can react negatively if your puppy is on any other medications. It can produce negative side effects in dogs that have glaucoma, cardiovascular disease, hyperthyroidism or prostatic disease For proper dosage, a dog that weighs under 30lbs should be administered a 10 mg dose every 8 hours, and dogs between 30lbs - 50lbs should be given a 25 mg dose. Consult your veterinarian for more information.