Published dose range
The published veterinary reference range for diphenhydramine in dogs is 2-4 mg per kg of body weight, given every 8-12h. In practice: 1 mg per lb (2.2 mg/kg).
Source: Merck Veterinary Manual →Plain diphenhydramine ONLY, combination products (with decongestants or acetaminophen) are dangerous. Drowsiness expected.
Skip it or ask a vet first if
glaucomaurinary obstructionwith sedativescombination cold products
If you think you overdosed
Call the Pet Poison Helpline: 855-764-7661 or ASPCA Poison Control: 888-426-4435. Both are staffed 24/7 by veterinary toxicologists.