The general dosage guideline for dogs is 1mg of Benadryl for every one pound of body weight. You should always consult your veterinarian, as there are a. The average dosage included in one Benadryl tablet is 25mg, so a pound dog should be given one tablet. Check the dosage on the package, and don't. the dose for a 5 lb. dog = 2 mL of liquid Benadryl or 1/4 of a mg tablet 6 mL, 12 mL, or 20 mL syringe, or pill cutter depending on the size of your dog. Read the ingredients of the medication before giving it to your dog. Steer clear of liquid Benadryl. Benadryl is a relatively harmless drug that should be totally safe for your dog. Benadryl is also known to effectively treat hives in both dogs and humans. You can print and tape the dosages to the Benadryl bottle or keep it in the box with the bottle, along with the syringe. Many people forget that they are using medicines when applying topical products, but even though little is absorbed meaning side effects are rare, applying far too much can lead to overdose symptoms just as though you had used too many tablets or too much liquid.