Published dose range
The published veterinary reference range for diphenhydramine in cats is 1-2 mg per kg of body weight, given every 8-12h. In practice: 2-4 mg total per cat.
Source: Merck Veterinary Manual →Bitter; cats foam/drool at the taste. Paradoxical excitement possible.
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.