PupkeeperCaution
Dog ate antihistamines (diphenhydramine)? What to do
Caution. Antihistamines like diphenhydramine are safe only at a dose your vet sets; too much can cause sleepiness or agitation, drooling and a racing heart.
If your dog ate or touched this, call your vet or a pet poison line now
United States
Poison lines in other countries: United Kingdom, Australia, Canada, New Zealand
What to do now
- Call your vet or a pet poison line now.
- Keep the packaging and bring it, and check the label for a decongestant such as pseudoephedrine.
- Count how many tablets are missing.
Don't
- Don't give any antihistamine unless your vet tells you to and sets the dose.
- Don't make your dog vomit unless a vet tells you to.
Signs to watch for
- Sleepiness or depression
- Agitation or hyperactivity
- Drooling
- Fast breathing
- Fast heart rate
Why
Vets sometimes use antihistamines, but the right dose depends on the dog. Many allergy and cold products also contain a decongestant such as pseudoephedrine, which can be dangerous for dogs.
Sources
Guide reviewed 9 October 2026.
General information from the sources above, not a diagnosis. When in doubt, call your vet.