Antihistamine Toxicity, Pseudoephedrine
Antihistamines are commonly used for allergies in people — and are sometimes prescribed by veterinarians for dogs.
The danger arises when owners give combination products meant for humans, especially those labeled with a “D” (Antihistamine-D). These contain pseudoephedrine, a potent decongestant that is extremely toxic to dogs even in small amounts.
Why Are “D” Medications So Dangerous?
Pseudoephedrine acts as a stimulant, causing a rapid increase in heart rate and blood pressure. In dogs, even half of a human tablet can lead to severe poisoning, Exposure can even be fatal, depending on the dose and the size of the dog.
Who’s Most at Risk?
All docs are susceptible to signs from this exposure, even at small doses
Small dogs (toxic dose reached quickly)
Dogs with heart disease or hypertension
Any dog with access to cold or allergy medications left on counters, purses, or nightstands
Signs of Pseudoephedrine Toxicity
Symptoms can start within 30 minutes and progress quickly:
Agitation or restlessness
Rapid heart rate or pounding heartbeat
Tremors or seizures
High blood pressure, panting, or collapse
Dilated pupils and vomiting
What To Do If Your Dog Is Exposed
Check the packaging immediately — if it lists pseudoephedrine or has a “D” in the name, treat it as an emergency.
Never induce vomiting at home without consulting a veterinary professional — some medications can cause harm if vomited back up.
Do not wait for symptoms. Call animal poison control immediately
ASPCA Animal Poison Control (888) 426-4435
Bring the medication packaging to the veterinary clinic — knowing the exact product and strength helps guide treatment.
Important Reminder
Never give over-the-counter human medications to your dog without consulting your veterinarian. If your veterinarian does recommend an antihistamine, always read the packaging closely to ensure the medication does not contain pseudoephedrine or other added ingredients.
Prevention Tips
Double-check medication labels before use.
Avoid “multi-symptom” or “D” products entirely.
Keep all human medications securely stored out of reach of pets.
Final Thoughts
Plain antihistamines can be useful in veterinary medicine, but combination products containing pseudoephedrine are dangerous — even deadly — for dogs. Always check with your veterinarian before giving any medication, and keep the ASPCA Animal Poison Control number saved where you can find it quickly. Quick action can save your pet’s life in an emergency.
