If your dog is unlucky enough to be stung by a bee or bitten by a mosquito, of course you’ll want to ease their itching and prevent your dog from having an allergic reaction. Since Benadryl is a go-to over-the-counter medicine for people, is it safe to give a dog Benadryl? The answer is yes, but you should first consult with your vet on the proper dog Benadryl dosage, and then you’ll need to make sure that there are no other active ingredients besides diphenhydramine. Do not give Benadryl to dogs with glaucoma, high blood pressure or cardiovascular disease. Benadryl can help dogs having allergic reactions to insect bites or stings and can help some dogs with motion sickness. Giving a dog Benadryl can also help with environmental allergies, but if your dog has allergies, talk to your veterinarian about prescription pet allergy medication that might help.