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 →Published range by weight
| Weight | Diphenhydramine (published range) |
|---|---|
| 5 lb dog | 4.5-9.1 mg |
| 10 lb dog | 9.1-18 mg |
| 20 lb dog | 18-36 mg |
| 30 lb dog | 27-54 mg |
| 40 lb dog | 36-73 mg |
| 50 lb dog | 45-91 mg |
| 60 lb dog | 54-109 mg |
| 80 lb dog | 73-145 mg |
| 100 lb dog | 91-181 mg |
Computed from the published 2-4 mg/kg reference range, every 8-12h. Product strengths rarely split evenly, so round DOWN to the nearest practical dose and confirm with your vet.
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.