Antihistamine Dosage for Cats

Posted by Lianne McLeod D.V.M. on

antihistamines for cats by Dr. Lianne McLeod

Cats, much like humans, can suffer from numerous health issues, one of which is allergies.  Allergies in cats may take many shapes, from minor distress to severe reactions that necessitate urgent medical attention.  It is thus vital for any cat guardian to have an awareness of allergies in cats, their causes, signs, and treatment methods.  Doing so enables early identification, suitable therapy, and maybe even avoidance of allergic outbursts in cats.

In this article, we shall dig deep into the realm of allergies in cats, investigating their reasons, characteristics, and treatment alternatives.  We will examine how the immune system’s extreme response to allergens can bring about an assortment of manifestations, going from mellow distress to serious, conceivably life-threatening responses.  Next, we'll look at the job of antihistamines, for example, Benadryl, in lessening these side effects and the significance of consulting a vet to distinguish the allergen causing the reaction and formulating an inclusive treatment plan.

Understanding Allergies in Cats

Allergies are a familiar concern for cats as well as for people.  But what truly are allergies?  At its foundation, an allergy is a reaction that the immune system of the body has to a usually harmless material, referred to as an allergen.  This overreaction is caused by misidentifying the allergen as a danger which stimulates the body into a protective action.  Commonly, this action leads to observable symptoms which we recognize as an allergic outburst.

In felines, the immune system carries out a vital responsibility in shielding the body against malice agents such as microorganisms and viruses.  Nevertheless, when it comes to an allergy, the immune system incorrectly recognizes a benign material as hurtful and reacts as such.  This reaction consists of discharging various chemicals, which include histamines, resulting in redness and other indications connected with allergies.

Common Allergens for Cats

Cats may display an allergic reaction to an assortment of products.  Popular allergens experienced by felines include:

Food Allergies: Some cats may develop allergies to certain types of food.  These foods can include various types of meat, dairy products, grains, and more.  Food allergies in cats can cause a variety of symptoms, including skin irritation, gastrointestinal issues, and more.

Cat food

Environmental Allergens:  Cats can also be allergic to various environmental substances.  These substances can include pollen from trees, grasses, and flowers, dust mites, mold spores, and more.  These allergens can cause symptoms such as sneezing, itchy skin, and watery eyes.


Flea Allergies:  Flea allergy dermatitis is a common condition in cats caused by an allergic reaction to flea saliva.  This allergy can cause severe itching and discomfort, leading to skin damage and secondary infections if not treated promptly.


It is important to note that each cat is unique, and what causes an allergic reaction in one cat may not cause the same severe allergic reaction in another.  Therefore, identifying the specific allergen causing your cat’s allergic reaction may require some detective work and the help of a veterinarian.

Symptoms of Allergies in Cats

The symptoms of allergies in cats can vary widely, depending on the type of allergen and the cat’s individual reaction to it.  However, some common symptoms of allergies in cats include:

Skin Symptoms: One of the most common signs of allergies in cats is skin irritation.  These symptoms include redness, swelling, and itching.  Cats with skin allergies may scratch or lick excessively at the affected areas, causing further irritation and potentially leading to skin infections.

Respiratory Symptoms:  Cats with allergies may also exhibit respiratory symptoms.  These symptoms include sneezing, coughing, and wheezing.  In severe cases, cats may experience difficulty breathing, which requires immediate veterinary attention.

Gastrointestinal Symptoms:  Some cats with allergies may experience gastrointestinal symptoms.  These symptoms include vomiting, diarrhea, and loss of appetite.

sick cat

Behavioral Changes:  Cats with allergies may also exhibit changes in behavior. These changes include increased grooming, restlessness, and changes in mood or temperament.

If you notice any of these symptoms in your cat, it is important to seek veterinary care.  Your vet can help determine the cause of your cat’s symptoms and recommend appropriate treatment options.  Remember, while allergies can be uncomfortable and distressing for your cat, they can often be managed effectively with the right treatment and care.

What is Benadryl?

Diphenhydramine, also known as Benadryl, is an early-generation antihistamine.  It is frequently used for reducing the effects of allergies, hay fever, colds, and other cases where an antihistamine response is wanted.

Benadryl is accessible in various forms, consisting of tablets, capsules, gels, creams, and liquids.  The oral preparations are employed to reduce internal complaints such as sneezing, runny nose, itchy or watery eyes, hives, skin rash, itching, and other allergic reactions.  The external formulations, like creams and gels, are used to soothe external representations such as itching, hives, and eruptions resulting from insect stings, sunburns, or slight skin discomforts.

How Benadryl Works

Benadryl performs by inhibiting the operation of histamine, a compound in the body that is let go during an allergy.  Histamine is answerable for many of the indications that occur during an allergy, like swelling, irritation, and flush.  By prohibiting the operation of histamine, Benadryl aids in pacifying these reactions.

benadryl for cats

Uses of Benadryl in Veterinary Medicine

In veterinary medicine, Benadryl is often used to treat symptoms of allergies in animals, including cats.  It can help to relieve symptoms such as itching, swelling, and redness that are associated with allergic reactions.

In addition to treating allergies, Benadryl is also used in veterinary medicine for its sedative properties.  It can be used to help calm animals that are anxious or stressed, such as during travel or after surgery.

However, it is important to note that while Benadryl is generally safe for use in animals, it should always be used under the guidance of a veterinarian.  The dosage required can vary depending on the size, weight, and overall health of the animal, and using too much can lead to serious side effects.  

Therefore, if you are considering using Benadryl for your cat, it is important to first consult with your veterinarian.  They can provide guidance on whether this medication is the right choice for your cat and if so, provide information on the correct dosage to use.

Is Benadryl Safe for Cats?

Benadryl, or diphenhydramine, is generally considered safe for use in cats.

happy cat

However, as with any medication, there can be potential risks and side effects.  Some cats may experience side effects such as sedation, dry mouth, urinary retention, or gastrointestinal upset. In rare cases, cats may have an allergic reaction to Benadryl itself.

It is also important to note that certain conditions can make the use of Benadryl more risky in cats.  For example, cats with glaucoma, high blood pressure, cardiovascular disease, or those who are pregnant or nursing should not take Benadryl unless specifically directed by a veterinarian.

Furthermore, Benadryl should not be used in conjunction with certain other medications without veterinary approval, as it can lead to negative drug interactions.   For instance, combining Benadryl with certain types of antidepressants, sedatives, or other antihistamines can potentially lead to increased sedation or other adverse effects.

Benadryl Dosage for Cats

The correct dosage of Benadryl for cats is typically determined based on the cat’s weight.  The general guideline is to give 1 milligram of Benadryl for each pound of body weight.  For instance, if your cat weighs 10 pounds, you would give 10 milligrams of Benadryl.  However, the dosage can vary depending on what Benadryl is being used to treat, and cats may take Benadryl up to three times a day every eight hours in a 24-hour period.

general rule for antihistamines for cats

Follow the Vet’s Recommended Dosage

While the general guideline provides a starting point, it is crucial to follow your veterinarian’s recommended dosage.  Each cat is unique, and factors such as age, overall health, and the severity of the allergic symptoms can influence the appropriate dosage.  Your vet is best equipped to determine the safest and most effective dosage for your cat’s specific needs.

Furthermore, it is imperative to only administer ordinary Benadryl to your feline.  Certain variants of Benadryl contain additional ingredients, including decongestants, which can be potentially harmful to cats.  Before giving any treatment to your pet, be sure to thoroughly examine the ingredients of the medication.

Risks of Benadryl Overdose

Like any other treatment, exceeding the recommended amount of Benadryl, such as one milligram more, can cause an overdose.  Symptoms that can result from a Benadryl overdose include restlessness, fast breathing, severe panting, and profound drowsiness.

In the worst cases, an overdose can cause seizures or even put the cat in a comatose state.  Therefore, if you think your pet might have taken an excess dosage of the drug, it is essential to seek help from a veterinarian promptly. An overdose is a dangerous affair that needs to be treated immediately.

Different Forms of Benadryl

Benadryl comes in various forms, including tablets, capsules, and liquid.  Each form has its own advantages and disadvantages, and the best choice will depend on your cat’s specific needs and preferences.

forms of benadryl treatment

Tablets and Capsules:  These are typically the most common form of Benadryl and are easy to store and transport.  However, they can be difficult to administer to some cats, especially if the cat is resistant to taking pills.

Liquid:  Liquid Benadryl can be easier to administer to cats, especially if mixed with a small amount of food or a treat.  However, it is important to ensure that the liquid formulation does not contain any ingredients that are harmful to cats, such as alcohol or xylitol.

Tips for Administering Benadryl

Administering medication to a cat can be challenging, but there are several strategies that can make the process easier:

Mix cat Benadryl with Food:  One of the easiest ways to administer Benadryl to your cat is to mix it with a small amount of their favorite food.  This mix can help mask the taste of the medication and make it more appealing to your cat.

Use a Pill Dispenser:  If you are using tablet or capsule form, a pill dispenser can be a useful tool.  These devices can hold the pill and allow you to place it directly into the back of the cat’s mouth.

Follow with a Treat:  After successfully administering the medication, give your cat a treat.  This trick can help make the experience more positive for your cat and make future medication administration easier.

Be Calm and Patient:  Cats can pick up on our emotions, so try to remain calm and patient throughout the process.  If your cat becomes too stressed or agitated, it may be best to take a break and try again later.

Remember, it’s important to always follow your veterinarian’s instructions when administering medication to your cat.  If you are having trouble administering Benadryl to your cat, do not hesitate to reach out to your vet for advice.

Potential Side Effects of Benadryl in Cats

side effects of excess antihistamines for cats

While Benadryl is generally safe for cats, it can cause some side effects. Some of the more common side effects that you might notice in your cat include:

  • Sleepiness:  Sleepiness is one of the most common side effects of Benadryl.  Your cat may appear drowsy or less active than usual.

  • Agitation:  In some cases, instead of causing sedation, Benadryl may cause your cat to become unusually excited or agitated.

  • Dry Mouth:  Benadryl can cause your cat’s mouth to become dry.

  • Difficulty Urinating:  Some cats may have trouble urinating after taking Benadryl.

  • Drooling:  Drooling can occur as a result of the dry mouth side effect.

  • Diarrhea:  Some cats may experience gastrointestinal upset, including diarrhea, after taking Benadryl.

  • Vomiting:  Vomiting is another potential gastrointestinal side effect.

Serious Side Effects

serious side effects of excess antihistamines for cats

In rare cases, cats may experience more serious side effects from taking Benadryl. These can include:

  • Depression or Hyperexcitability:  In some cases, Benadryl can cause changes in your cat’s mood or behavior.

  • Decrease in Urination:  If your cat is urinating less than usual after taking Benadryl, it could be a sign of a more serious problem.

  • Loss of Appetite:  If your cat is eating less than usual, it could be a side effect of Benadryl.

If your cat experiences any of these serious side effects, it is important to seek veterinary care immediately. Do not let allergies get the best of your feline friend! Discover our range of antihistamines specially formulated for cats. Act now and ensure your cat’s comfort and well-being.


  1. Mitchell, S. C., DVM, & DABVP. (2022). Can you give cats Benadryl? The Best Pet Health & Care Advice from Real Vets | PetMD.

  2. Felton, A. (2022, December 14). What to know about antihistamines for cats. WebMD.

  3. Diphenhydramine for dogs and cats: Uses, dosage & side effects. (2022). Veterinary Pharmacy for Compounded Pet Medications.

  4. Crivineanu, Maria; Dobre, Ionuț-Răzvan; Rotaru, Elena; Păunescu, Ileana. (2017). The effect of antihistamines on allergic inflammation and anxiety in dogs and cats.

  5. Caitlin E. Older, Alison Diesel, Adam P. Patterson, Courtney Meason-Smith, Timothy J. Johnson, Joanne Mansell, Jan S. Suchodolski, and Aline Rodrigues Hoffmann. (2017). Cutaneous hypersensitivity dermatoses in the feline patient: A review of allergic skin disease in cats. PubMed Central (PMC).

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Lianne McLeod, DVM, is a former writer for The Spruce Pets, contributing articles for 11 years. Before Dr. McLeod began writing about pet care, she worked several years in small animal practice. She has written extensively about the care and keeping of exotic pets and pet health care. She now researches water quality and chronic disease at the University of Saskatchewan. Lianne McLeod earned her Doctorate of Veterinary Medicine from the Western College of Veterinary Medicine at the University of Saskatchewan. She also received a Bachelor of Science degree in biology from Simon Fraser University. She continued her education and received a Ph.D. in Epidemiology from the University of Saskatchewan. Now, she splits her time between her family, research and writing about pet health for all the animal lovers out there.
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