Chlorpheniramine for Cats and Dogs

Updated Mar. 21, 2024

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PetMD’s medications content was written and reviewed by veterinary professionals to answer your most common questions about how medications function, their side effects, and what species they are prescribed for. This content shouldn’t take the place of advice by your vet.

What Is Chlorpheniramine for Cats and Dogs?

Chlorpheniramine is an over-the-counter human antihistamine that can be given to dogs and cats with allergies or itching associated with certain types of skin hypersensitivity.

Chlorpheniramine is used in dogs but is more widely used in cats, ferrets, and birds. Chlorpheniramine works in dogs and cats best if given long-term to prevent allergies, as it is not very effective for flare-ups of allergy symptoms.

Chlorpheniramine does not cure your pet’s underlying allergic condition, but may help relieve the itching and inflammation triggered by it. Chlorpheniramine is often used in combination with other allergy management treatments. It often takes time and patience—your veterinarian will recommend a treatment regimen that is appropriate for your pet.

Chlorpheniramine is FDA-approved for human use in many oral formulations, including tablets, syrup, and extended-release tablets, under the brand names Aller-Chlor® and Chlor-Trimeton®, and as generic chlorpheniramine. It is also used in over-the-counter and prescription products.

It is currently not FDA-approved as a veterinary medication. However, it is readily utilized in the veterinary field, and veterinarians can legally prescribe or recommend certain human drugs for use in animals in certain circumstances. This is called extra-label or off-label use, because this use isn’t described on the drug label.

Speak with your veterinarian about which product is right for your pet. Your vet may recommend products that only contain chlorpheniramine as the single active ingredient, as combination chlorpheniramine products may also contain other decongestants, cough suppressants, and pain relievers that are toxic to dogs and cats. Your vet may also recommend against extended-release tablets due to unpredictable absorption in the body and because commercially available dosages for humans are usually different from those prescribed for your pet by a veterinarian.

In certain circumstances, your veterinarian may prescribe a compounded formulation of chlorpheniramine. Compounded medications are prescribed if there’s a specific reason your pet’s health can’t be managed by an FDA-approved drug, such as if your pet has trouble taking pills in capsule form, the dosage strength is not commercially available, or the pet is allergic to an ingredient in the FDA-approved medication. Compounded medications are not FDA-approved. They are created by either a veterinarian or a licensed pharmacist on an individual basis to best suit a patient’s particular needs. You can learn more about compounded medications here.

Chlorpheniramine Considerations

Chlorpheniramine should be used with caution in pets with a certain type of glaucoma, high blood pressure, gastrointestinal or urinary obstruction, hyperthyroidism, heart disease, prostate enlargement, and certain types of respiratory conditions, and in pets who are hypersensitive to it and other antihistamines. Use it with caution in nursing pets, as it is excreted into breast milk.

Chlorpheniramine may cause dogs to feel sleepy or groggy, so it may not be an ideal choice for working or assistance dogs because it can reduce their awareness.

Giving chlorpheniramine with certain medications may result in health risks to your pet, so it is important to discuss your pet’s medications, including vitamins and supplements, and medical conditions with your veterinarian.

How Chlorpheniramine Works in Cats and Dogs

Chlorpheniramine belongs to a class of medications called antihistamines. The body’s immune system releases a naturally occurring chemical called histamine to protect the body by responding to triggers (allergens) such as insect stings, parasites, or pollen.

Histamine works to remove the allergen and can cause inflammation or pain, increase heart rate, dilate blood vessels, and increase stomach acid production in the process. Pets produce other chemicals similar to histamine that also contribute to allergic reactions, which is why antihistamines such as chlorpheniramine tend to be less effective in pets than in humans.

Chlorpheniramine Directions for Cats and Dogs

Follow the directions on the drug label or as provided by your veterinarian. Chlorpheniramine is typically given by mouth two to three times a day. Chlorpheniramine’s bitter taste may make it difficult to administer to pets. Some may become drowsy while on this medication, but the sedative effect typically lessens over time.

Missed a Dose?

Speak with your veterinarian about what to do if you forget to give a dose of chlorpheniramine. Generally, they will advise you to give it when you remember, or if it is almost time for your next dose, to skip the missed dose and resume your normal dosing schedule. In most cases, do not give extra or double doses.

Chlorpheniramine Possible Side Effects in Cats and Dogs

The most common side effect of this medication is drowsiness, but the sedative effect typically lessens over time.

Additional side effects include:

  • Vomiting

  • Diarrhea

  • Loss of appetite

  • Constipation

  • Dry mouth

  • Excitement (especially in cats)

  • Drooling (especially in cats – due to the bitter taste)

Human Side Effects

Chlorpheniramine is an over-the-counter medication for humans, frequently with dosages different from those prescribed for your pet by a veterinarian. Due to possible side effects, humans should never use medicine dispensed for their pets and pets should not be given any medicine dispensed for a human’s use.

If you accidentally ingest a pet medication, call your physician or the national Poison Control Center hotline at 800-222-1222.  


No specific monitoring is required for this medication, but your veterinarian may recommend routine testing depending on your pets' individual needs, other medications they may be on, or the issue that initially caused your pet to be placed on this medication.

Call Your Vet If:

  • Severe side effects are seen (see above)

  • Your pet’s condition worsens or does not improve with treatment

  • You see or suspect an overdose

You have additional questions or concerns about the use of chlorpheniramine.

Chlorpheniramine Overdose Information for Cats and Dogs

While chlorpheniramine is generally safe to use in pets, overdoses can occur. Symptoms of an overdose include:

  • Excitability/agitation

  • Seizures

  • Fatigue (Lethargy)

  • Loss of coordination

  • Coma

  • Dangerously low breathing or heart rate

  • Severe dry mouth

If you suspect an overdose, immediately contact your veterinarian, seek emergency veterinary care, or contact an animal poison control center. Consultation fees often apply.

Pet Poison Helpline (855) 764-7661

ASPCA Animal Poison Control (888) 426-4435

Chlorpheniramine Storage for Cats and Dogs

Chlorpheniramine should be stored according to the medication label and at 77 F. Brief exposure to temperatures 59-86 F is acceptable. Keep the container tightly closed to protect this medication from moisture and light.

Compounded medications should be stored according to the compounding pharmacy’s label.

Keep out of reach of children and pets.


Does chlorpheniramine make pets sleepy?

One of the known side effects of chlorpheniramine is that it may make your pet sleepy. Slight drowsiness will usually decrease in severity the longer your pet is on this medication. If your pet is excessively sleepy, speak with your veterinarian about changing the dose of this medication or using an alternative product. If your pet is unable to be roused from sleep, this could be an emergency. Contact a veterinarian immediately or seek emergency veterinary care.

Can you crush chlorpheniramine for cats?

No, you should not crush chlorpheniramine for cats, as it has a bitter taste that cats do not tolerate. Speak with your vet first to ensure this medication is appropriate for your cat, and ask about a compounded formulation that would be easier to administer to your cat.

What symptoms does chlorpheniramine treat in cats?

Chlorpheniramine is used in cats to treat the symptoms of itching and irritation associated with allergies and certain types of skin hypersensitivity.


Eichenseer M, Johansen C, Mueller RS. Efficacy of dimetinden and hydroxyzine/chlorpheniramine in atopic dogs: a randomised, controlled, double-blinded trial. Veterinary Record. 2013;173(17):423.

No vet writer or qualified reviewer has received any compensation from the manufacturer of the medication as part of creating this article. All content contained in this article is sourced from public sources or the manufacturer.

Featured Image: Pevide



Stephanie Howe, DVM


Stephanie Howe, DVM


Dr. Stephanie Howe graduated from the University of Florida College of Veterinary Medicine in 2011, after receiving a Bachelor of Science...

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