Question: how long till benadryl kicks in for hives?
Answer: Antihistamine medicine The main side effect of this drug is drowsiness in some people. Other antihistamines (for example, store brands of any drug for hay fever) will also help. When you give Benadryl, give it 3 to 4 times a day until the hives are gone for 12 hours. Use the dosage given on the product.