How much Benadryl should I give? The standard dosage for oral Benadryl is 1 mg per pound of body weight, given 2-3 times a day. Most drug store diphenhydramine tablets are 25 mg, which is the size used for a 25 pound dog. My dog is about 35 to 40 pounds how much benadryl - Answered by a verified Dog Specialist We use cookies to give you the best possible experience on our website. By continuing to use this site you consent to the use of cookies on your device as described in our cookie policy unless you have disabled them. Benadryl dosage for dogs - I've heard that you can give benadryl to a dog, so how much should I give to my dog with allergies - weighs around 25 lbs. Benadryl is an over-the-counter medicine that can be given to dogs. Diphenhydramine, the most common active ingredient, is an H 1 antagonist, which means it helps to prevent the uptake of histamine (a type of substance responsible for allergic reactions) by receptors in the body. I have a 55lb dog and liquid benadryl would be no more than 1/4tsp MAX for this si … ze, and that's almost too much. The above is not accurate. Standard dosage for dog is is 1 mg of benadryl. By continuing to use this site you consent to the use of cookies on your device as described in our cookie policy unless you have disabled them. Give 1mg of Benadryl per pound such that if your dog weighs 30pounds, you should give it 30 mg of Benadryl. The general guideline on how much Benadryl can I give my dog stipulates that you give it to your dog to control allergic reactions such as itching, stuffy nose, running nose, sneezing, ear infections and coughing. How Much Benadryl For 35 Lb Dog - petsmart. PetSmart - Official SiteAt PetSmart, we never sell dogs or cats. Together with PetSmart Charities, we help save over 1,500 pets every day through adoption. So a 35-pound dog should get 35 mg of Benadryl per dose. The Benadryl dose for 16 lb dog would be 16mg. Ask your vet for more help with dosing frequency, but the typical dose is 3 times a day, every 8 hours apart.