How Much Benadryl Can I Give My Dog?

The standard dose of Benadryl (plain diphenhydramine) for dogs is about 1 mg per pound of body weight, given every 8 to 12 hours — up to two or three times a day. For a quick, exact number, use the Dog Benadryl Dosage Calculator.

Quick dose by weight

Because most tablets are 25 mg, the math usually works out cleanly:

• 10 lb dog → ~10 mg (about ½ of a 25 mg tablet, or use liquid)
• 25 lb dog → ~25 mg (one 25 mg tablet)
• 50 lb dog → ~50 mg (two 25 mg tablets)

For smaller dogs, children’s liquid diphenhydramine (12.5 mg per 5 mL) is easier to measure accurately than splitting tablets.

Use plain diphenhydramine only

This is the rule that matters most. Avoid any product labelled “-D”, “Allergy Plus Congestion”, “Sinus”, or “Severe” — these contain decongestants (pseudoephedrine), pain relievers (acetaminophen), or alcohol that can seriously harm dogs. Also confirm the label does not list xylitol, which is toxic to dogs.

How often and how long

Benadryl can be given every 8–12 hours for short-term relief of mild itching, allergic reactions, or motion sickness. It typically works within about 30 minutes; mild drowsiness is the most common effect. For daily or long-term use, talk to your veterinarian first.

When to call your vet instead

Skip the home dose and contact a vet right away if your dog is having a severe allergic reaction (facial swelling, hives spreading quickly, trouble breathing), is a very young puppy, is pregnant, or has glaucoma, heart disease, or high blood pressure.

This guide is educational and not veterinary advice. Always confirm the dose and suitability with your veterinarian.