Dog medicine dose calculator for common over-the-counter drugs

Which human medicines can dogs take?

A handful of over-the-counter medicines have dose ranges for dogs published in veterinary references, and vets sometimes suggest them by phone. This calculator covers four: three antihistamines for allergies and one acid reducer. It shows the range as published and tells you where sources disagree.

dose (mg) = weight in kg × mg per kg

Worked example: a 30 lb (13.6 kg) dog on cetirizine at 1 to 2 mg/kg needs 14 to 27 mg, which is 1.5 to 2.5 of a 10 mg tablet once a day, if the vet agrees.

Diphenhydramine (Benadryl) for dogs

An older, sedating antihistamine used for allergic reactions, motion sickness and mild sedation. The AAHA 2023 guidelines list 2 to 3 mg/kg every 12 hours, and Merck 2 to 4 mg/kg every 8 to 12 hours. Use plain diphenhydramine only, never “Plus Congestion”, Sinus or PM products. Our Benadryl dosage calculator goes into more detail, including a chart by weight.

Cetirizine (Zyrtec) for dogs

A newer antihistamine used for itching from allergies, hives and insect bite reactions. AAHA lists 1 to 2 mg/kg once a day; Merck gives 1 mg/kg (or 10 to 20 mg per dog) every 12 to 24 hours. VCA Animal Hospitals warns never to give the cetirizine and pseudoephedrine combination (Zyrtec-D) to dogs, and to use plain cetirizine with caution in dogs with seizures, kidney, liver or heart disease, glaucoma, urinary retention, thyroid or prostate problems, and in pregnant, nursing or senior dogs. Possible side effects are vomiting, rarely drooling, and sleepiness in small dogs at higher doses.

Loratadine (Claritin) for dogs

A second-generation antihistamine, like cetirizine. The Merck second-generation antihistamine table gives 0.25 to 1.1 mg/kg once a day, while the AAHA guidelines list 1 mg/kg every 12 hours; the calculator uses Merck's once-daily range. Merck notes that loratadine is often sold combined with pseudoephedrine, which makes an overdose far more dangerous, so avoid Claritin-D in all its versions. The human Claritin label asks people with liver or kidney disease to check with a doctor first, and the same caution makes sense for dogs.

Famotidine (Pepcid) for dogs

An acid reducer vets use for stomach ulcers and acid reflux. Merck lists 0.5 to 1 mg/kg once a day, but the ACVIM consensus statement found that once-daily dosing gives little benefit for ulcers or reflux and that studies used it every 12 hours, so the calculator shows “every 12 to 24 hours” and leaves the timing to your vet. According to VCA Animal Hospitals, it is best given on an empty stomach before a meal, needs caution in older dogs and those with liver, kidney or heart disease or that are pregnant, and interacts with azole antifungals, some antibiotics (cefpodoxime, cefuroxime), cyclosporine and iron. Vomiting blood, black stools or repeated vomiting need a vet, not an antacid.

Medicines this calculator leaves out on purpose

Ibuprofen, naproxen, aspirin and acetaminophen are not here. They have narrow safety margins in dogs and cause stomach ulcers, kidney failure or liver damage at doses an owner could easily give by mistake. If your dog has already swallowed one, use the painkiller toxicity calculator and call a poison hotline. Cold and sinus products are left out too, because their decongestants (pseudoephedrine, phenylephrine) are dangerous to dogs. For anything else, check the is it toxic to dogs checker.