My Vet Said To Give My Dog A Half Dose Of Benadryl A Day For His Itching. Is That A Half Of An Adult Dose?

You should really check with you vet so that you don't give your dog an overdose It will depend on the size and weight of the dog as to how much should be given.

How much does your dog weigh? How old is your dog? My doberman weighs 75 lbs, and is one year old, and the full dosage for Benadryl is
25 mg, one 2 x per day. If your vet said to use 1/2 dose, split the pink caplet. You should use the pink CAPLETS, not the CAPSULES.
Also, ask your vet for a calming shampoo to use on your dog to bath him and calm inflammation from itching. The REASON your dog is itching should be found as well, so as not to just treat the symptoms, but also the source.  Let us know how your dogchild is doing! Nice to see a fellow dog lover on BLURTIT!!

The dose of Benadryl is 1 milligram per pound of body weight given by mouth 2-3 times a day.  Some veterinarians will not give more than 50 milligrams per dog.  Benadryl comes in 25 milligram capsules and a Children's Liquid.  Do NOT use the Cold and Sinus variety--only plain Benadryl is ok.
Talk to your veterinarian to find out if they meant half of the dog or human dose.  It is best to follow the treatment plan your veterinarian laid out as this is who you will be following up with.