Antihistamines for Cats: Dosage and Side Effects

Antihistamines for cats help to control different allergic conditions, such as itching and asthma, but they must be prescribed by a veterinarian. Never give your pet a drug for human use.
Antihistamines for Cats: Dosage and Side Effects
Samuel Sanchez

Reviewed and approved by the biologist Samuel Sanchez.

Last update: 27 December, 2022

Those who suffer from different allergies are familiar with antihistamines. Because of this, it’s easy to think that the way out of an allergy problem in cats would be to provide them with a dose of these medications. However, whatever the case, it’s never a good idea to self-medicate pets, and you should always get a professional opinion. Find out all about antihistamines for cats.

For example, when people have allergy symptoms, the best step is to perform tests that allow vets to establish the exact origin of the allergy. They will carry out skin evaluations, which consist of extracting small samples of purified allergen extracts to identify how the skin reacts.

They will also perform blood tests in order to identify the presence of specific antibodies and indicate the degree of sensitivity to a certain allergen. In the case of cats, the veterinarian will also need to map out a diagnostic pathway to include the tests necessary to establish treatment, which may or may not require antihistamines.

What are antihistamines for cats used for?

As the Mayo Clinic indicates, antihistamines are part of the normal drug treatment for pet allergies that humans suffer. These medications help to alleviate the symptoms that trigger allergies. Among them, we find sneezing, watery eyes, nasal congestion, cough, facial pressure, and mucous discharge.

A manual on veterinary pharmacology from the National Agrarian University of Nicaragua explains that, whenever there’s an allergy, histamine is released. This is the substance that causes symptoms such as allergic itching, coughing, sneezing, runny nose and eyes, vomiting or diarrhea. Antihistamines block its action and promote the well-being of the patient.

Other articles on animal health explain that the use of antihistamines is common in the control of allergic pruritus in cats and dogs. Experts believe that one of the reasons that first-generation antihistamines are able to reduce scratching could be due to their sedative action. In the specific case of cats, this same study indicates that Chlorpheniramine is effective in 80% of cases.

In addition to controlling allergic pruritus, these medications can also manage feline asthma, although this isn’t the only drug that vets use to treat allergic pathologies. For greater effectiveness, it’s usually combined with other compounds and control measures at home, once the origin of the allergy is identified.

A cat smells pills.

Dosage for cats

The type of antihistamine that a cat should receive in the event of a possible allergy must be prescribed by a veterinarian, as well as the dosage and the total length of the treatment. Of course, vets will treat each case as required.

For this same reason, you need to be careful with the brand of antihistamine that you buy for your cat. The reason being that the doses are not the same with every brand, and different strengths exist.

According to the MSD Manual Veterinary Manual, these are the most common antihistamine dosages recommended for cats:

  • Hydroxyzine: 0.5 to 2 milligrams for every kilo of weight.
  • Cyproheptadine: 0.25 to 0.5 milligrams for every kilo of weight 3 times a day or a single dose of 1.1 milligrams for every kilo of weight.
  • Chlorpheniramine: 2 to 4 milligrams 2 times a day.
  • Diphenhydramine: 2 to 4 milligrams for every kilogram of weight.

Trademarks of antihistamines for cats

Different brands of antihistamines for cats vary as far as the principal ingredient is concerned, and so does its concentration. This is why it’s so important to buy the brand indicated by the veterinarian. We tell you more about four of the most common types of antihistamines in the feline world.


This is a first-generation antihistamine that’s usually prescribed to manage allergic dermatitis and other types of conditions that require antihistamine action. In most cases, this drug solves the problem without the need to combine it with other drugs.


This medication is used to treat the itching and inflammation associated with allergies, as well as poisoning, asthma, and serotonin syndrome. It’s also useful to stimulate the appetite in sick and stressed cats. The objective is to prevent the animal from developing other types of diseases related to lack of nutrition.


This is one of the most common antihistamines. It’s one of the first generation types, and stands out for the few side effects it causes. It’s used to treat allergic pruritus and other types of allergic manifestations.


This antihistamine isn’t only used in cats, but is also indicated in dogs and other animals, such as ferrets and cattle. Its main utility is to control allergies with different origins. It’s administered orally in the form of tablets, capsules, or liquids, as well as for injection.

Although they may share the same name as antihistamines for human use, it’s important to reiterate that you shouldn’t give them to your cat or other pets. Before using any antihistamine on animals, discuss it with your vet.

Contraindications of antihistamines for cats

Giving antihistamines to cats without veterinary advice is dangerous, especially if you don’t know the exact condition of the animal. Like all medications, these drugs have contraindications that we must know about.

One of them – the most important – has to do with pregnant cats, in which antihistamines are counterproductive, as they can cause fetal malformations. They’re also contraindicated in cats with glaucoma, epilepsy or in those who are receiving other pharmacological treatments.

Likewise, technical datasheets specify that this type of medication shouldn’t be given to cats with hypersensitivity to the active component or any of its excipients. This would cause allergic reactions, and ultimately anaphylactic shock, leading to death.

All the relevant information must be provided to the veterinarian, who will make the decision whether to indicate antihistamine treatment or not. Just one more reason not to self-medicate pets.

Side effects

Studies indicate that the side effects of antihistamines are related to overdoses, as, normally, with an appropriate dose, they won’t occur. Among the possible adverse manifestations after the intake of antihistamines in cats, are the following:

  • Slowness
  • Drowsiness
  • Disorientation
  • Sedation or excitement

However, in cases where an overdose has occurred, symptoms such as ataxia, athetosis and seizures with mydriasis in the pupils and a fixed stare are evident. Given the appearance of these clinical signs, veterinary attention is urgent.

Depression in cats can be treated with medication.

Are there natural antihistamines?

Some plants have antihistamine properties that, as with the drugs that humans consume, aren’t suitable for pets. Some can even be counterproductive for them, in addition to the fact that this type of treatment usually complements the action of the drugs, and doesn’t provide definitive solutions.

On the other hand, we must remember that allergies aren’t usually cured, neither in humans nor in pets. Medicine keeps symptoms under control, but it’s just as important to take hygiene and care measures to avoid new allergic attacks. The vet will inform you more fully about the condition of your feline.

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Antihistamines are medications used for the ongoing treatment of allergies and they may be prescribed to dogs at some point.

All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.

  • ANTIHISTAMÍNICO SYVA. Ficha técnica del Departamento de Medicamentos veterinarios.
  • Antihistamine Dosages. MSD Manual Veterinary Manual.
  • Gómez, N., & Pisano, P., & Castillo, V., & Fontanals, A. (2012). Asma felino: fisiopatología, diagnóstico y tratamiento. InVet, 14(2),191-207.[fecha de Consulta 16 de Junio de 2021]. ISSN: 1514-6634. Disponible en:
  • Manzuc, Pablo (2008). Diagnóstico y Manejo a largo plazo del prurito. REDVET. Revista Electrónica de Veterinaria, IX(12), .[fecha de Consulta 16 de Junio de 2021]. ISSN: . Disponible en:
  • Farmacología veterinaria I. Universidad Nacional Agraria.
  • Alergia a las mascotas. Mayo Clinic.
  • Lizárraga, I., Sumano, H. Farmacología clínica de los antihistamínicos en medicina veterinaria. Vet. ´Méx. 29 (4) 1998.

The contents of My Animals are written for informational purposes. They can't replace the diagnosis, advice, or treatment from a professional. In the case of any doubt, it's best to consult a trusted specialist.