The weight-based rule
Benadryl is a brand name for diphenhydramine, a first-generation antihistamine. The widely cited guideline is about 1 mg per pound of body weight per dose (the Merck Veterinary Manual range is 2–4 mg/kg), given up to two or three times a day. This is general information, not a prescription — confirm the dose and whether it suits your dog with your vet.
Dose by dog weight
| Dog weight | Typical dose per giving | Frequency |
|---|---|---|
| 10 lb | ~10 mg | every 8–12 h |
| 25 lb | ~25 mg | every 8–12 h |
| 50 lb | ~50 mg | every 8–12 h |
| 75 lb | ~75 mg | every 8–12 h |
| 100 lb | ~100 mg | every 8–12 h |
Standard tablets are 25 mg; children's liquid is usually 12.5 mg per 5 mL. For the liquid, mL = dose in mg ÷ 12.5 × 5, so a 25 mg dose is 10 mL.
Before you give any
- Diphenhydramine only. Read the ingredients. Formulas with pseudoephedrine, acetaminophen or other actives can poison a dog.
- Ask the vet first. Puppies under about 4 weeks, pregnant or nursing dogs, and dogs with glaucoma, heart disease, or bladder or breathing problems need veterinary sign-off. Older dogs often need a reduced dose.
- Watch for trouble. Mild drowsiness is expected. Call a vet if you see facial swelling, laboured breathing, no urination for 12+ hours, agitation or a fast heartbeat.
Common questions
How much Benadryl can I give my dog?
The common guideline is about 1 mg of diphenhydramine per pound of body weight, up to two or three times a day. A 50 lb dog works out to roughly 50 mg per dose. Confirm the amount with your vet before giving it.
Can I use human Benadryl tablets?
Only if the label lists diphenhydramine as the sole active ingredient. Avoid any "sinus", "cold" or combination product, because pseudoephedrine and other added drugs are toxic to dogs.
How often can the dose be repeated?
Roughly every 8 to 12 hours, so no more than about three doses in a day. Do not shorten the interval to chase symptoms.
