Can you give a dog over the counter allergy meds. that is meant for humans, if so how much per 20 #.?

Yes, I only know of one allergy OTC medicine that you can use on dogs & cats:
-Benadryl (generic is diphenhydramine = cheaper).  The dose is one mg/pound.  Benadryl/diphenhydramine is sold in 25mg tablets & capsules.  So for a 20 lb dog, I would give one 25 mg tablet or capsule; 100 lb dog, give 4 tablets or capsules (100mg). This treatment can be repeated every 6-8 hours if needed.  Just hide the pills in some of their favorite treats and give them one pill at a time. It will probably make your dog sleepy, and drink a little more water/and urinate more than usual.  Benadryl/diphenhydramine is used to treat allergies, itching, and runny nose/cold symptoms.no you don't you have to take him to either a vet or buy him DOG MEDICINE. NEVER give him human meds.NEVER unless you want to explain why your dogs killed over on the middle of the living room floor.
Take him to a vet and buy a dog book.noMy vet has told me to give my dog a human Benadryl for itching. I have also used Amodium A.D. for severe diahrea. I don't know how much by weight but my dog is approx. 50 pounds.I have done this with several dogs and it worked for them. I don't want to tell you anything that would harm your dog. I'm only relating my experience.Benedryl was recommended for my dog by the vet. Read the label and give according to child dosage or weight.Call your vet office and someone will tell you on the phone.benadryl is on mg per lb. 20lbs, 20mg (25 is ok too.)Benadryl is also known as diphenhydramine and is used for atopy in dogs.  Please refer to your veterinarian's instructions for the dosage s/he would like you to administer your pet.