Benadryl dosage for dogs calculator

How much Benadryl can I give my dog?

Benadryl's active ingredient is diphenhydramine, an older antihistamine. The 2023 allergy guidelines from the American Animal Hospital Association (AAHA) list a dog dose of 2 to 3 mg per kg of body weight every 12 hours. The Merck Veterinary Manual gives a slightly wider range, 2 to 4 mg/kg every 8 to 12 hours. The calculator uses the overlap, 2 to 3 mg/kg, which is the range vets commonly use. Confirm it with your vet before giving it.

dose (mg) = weight in kg × 2 to 3

You may have heard “1 mg per pound”. That works out at 2.2 mg/kg, inside the same range. For a 25 lb (11.3 kg) dog, 2 to 3 mg/kg is about 23 to 34 mg: one standard 25 mg tablet.

Benadryl dosage chart for dogs by weight

Measure liquids with an oral syringe, not a kitchen spoon. For dogs over 100 lb, use the calculator and check the result with your vet.

Which Benadryl products can dogs have?

Only products whose Drug Facts box lists diphenhydramine as the only active ingredient. Standard Benadryl Allergy tablets and Liqui-Gels have 25 mg each, Extra Strength versions 50 mg, and the children's chewables and liquid 12.5 mg (the liquid per 5 mL). Store-brand diphenhydramine works the same way if the strength matches.

Never use these:

• Anything with a decongestant: “Plus Congestion”, “Sinus”, “Cold” or “-D” products (phenylephrine or pseudoephedrine)
• PM pain relievers such as Tylenol PM or Advil PM, which add acetaminophen or ibuprofen
• Any liquid, chewable or melt-in-the-mouth product with xylitol (also sold as birch sugar) in the inactive ingredients
• Itch creams, gels and sprays: they are for skin, not for swallowing

Decongestants are the biggest worry. Pseudoephedrine causes signs in dogs from 5 to 6 mg/kg and can kill at 10 to 12 mg/kg, and phenylephrine can raise blood pressure and cause vomiting. If your dog has already swallowed a combination product, use the painkiller toxicity calculator for PM products or the is it toxic to dogs checker, and call a poison hotline.

Which dogs should not have Benadryl?

VCA Animal Hospitals advises not using diphenhydramine in dogs that are allergic to it or in very young animals, and using it only with caution, meaning after talking to your vet, in dogs with:

• pregnant or nursing
• glaucoma
• heart disease or high blood pressure
• enlarged prostate
• bladder or bowel blockage
• overactive thyroid
• chronic lung disease (copd)
• senior dog
• working dog that must stay alert

It can also interact with sedatives, anesthetics, some pain medicines, tricyclic antidepressants and other anticholinergic drugs, so tell your vet everything your dog takes. If your dog is booked for allergy skin testing, stop diphenhydramine at least 2 weeks before.

What Benadryl does, and doesn't do, for dogs

Vets use diphenhydramine for allergic reactions, motion sickness, as a mild sedative and alongside treatment for mast cell tumors. It starts working within 1 to 2 hours. Common side effects are drowsiness, dry mouth, trouble peeing, vomiting, diarrhea and a smaller appetite; some animals become hyperactive instead of sleepy.

It is not a strong allergy drug. The AAHA guidelines flag its effect on itching as questionable when given by mouth, so if your dog scratches all year, ask about better options. For other over-the-counter medicines vets sometimes recommend, such as cetirizine, loratadine or famotidine, see our dog medicine dose calculator.

If your dog chews through a packet, an overdose of diphenhydramine can cause deep sleepiness or the opposite, agitation, plus a racing heart, vomiting, wide pupils, low blood pressure, tremors and sometimes seizures. Call your vet or a poison hotline, ASPCA Animal Poison Control at (888) 426-4435 or Pet Poison Helpline at (855) 764-7661 (both may charge a fee), and have the box ready: with combination products, the other ingredients often matter more than the antihistamine.