Before you give your cat anything to help with his itchiness, make sure you're treating the real cause.

If you suffer from allergies, you're probably familiar with the soothing effects of an antihistamine like Benadryl. But you may not know that it's possible to share that portion of your medicine cabinet with your itchy, sneezing cat. Benadryl is generally considered to be safe for cats and is sometimes used to treat allergies and allergic reactions in cats. However, as with any medical problem and treatment, it's important to reach out to your veterinarian for help before giving your cat anything out of their ordinary routine. 

What is Benadryl?

Benadryl is the brand name for diphenhydramine hydrochloride, a common over-the-counter antihistamine. Antihistamines like Benadryl are regularly used to treat allergy symptoms. They work by blocking histamine, which is a chemical released by the immune system that causes an allergic reaction (like itchiness) when the body comes into contact with an allergen. 

tabby cat scratching itself
Credit: Nils Jacobi / Getty

Why Would a Cat Need Benadryl?

Trent Eddy, DVM, of Ironhorse Veterinary Care in Leawood, Ks., says there are two main reasons you might need to give your cat Benadryl: general allergy issues or acute allergic reactions. Learn more about both below.

General allergy issues

Just like humans, cats can have allergic reactions to various things in the environment, such as pollen, cleaning products, and certain rubber and plastic materials. They can also have food allergies. Signs your cat may be experiencing allergies can include sneezing, itchiness, vomiting, and diarrhea. "However," Eddy says, "I generally feel that antihistamines as a solo agent are fairly ineffective at helping allergy issues. But we might try it as a potential low-cost option."

Acute allergic reactions

Acute allergic reactions could include facial swelling and hives in response to a bee sting, spider bite or vaccine. "I would definitely reach for Benadryl in these situations," Eddy notes. 

As in humans, Benadryl can also have a sedative effect in cats, but Eddy cautions that it can have the opposite effect as well: "Instead of calming your cat, your cat could become even more fired up," he says.

Finally, you could potentially use Benadryl to prevent motion sickness in your cat before riding in the car. Dramamine, or dimenhydrinate, is an antihistamine that's commonly used to prevent and treat motion sickness. It's actually a combination of two drugs, one of them being diphenhydramine (a.k.a. Benadryl). Eddy notes that while Benadryl can be tried for motion sickness with approval from your vet, there are much more effective options available to help keep Kitty from throwing up. 

How Much Benadryl Should I Give My Cat?

According to Eddy, the recommended dosage of Benadryl for cats is one to two milligrams per pound (or two to four milligrams per kilogram) every eight hours. If you're trying to determine what dosage of the antihistamine is safe for your cat, for example, and she weighs  around 12 pounds and you have a 25-milligram tablet, your cat can have the entire tablet or you can cut it in half. 

Are There Any Potential Safety Issues With Giving My Cat Benadryl?

While Benadryl is typically safe for cats, there are some steps you should take to protect your cat from potential problems:

Check with your veterinarian

It's always best to talk to your veterinarian before giving your cat any new medications—even an over-the-counter product like Benadryl. As the overseer of your cat's overall health, they are in the best position to point out potential problems. For example, Eddy says that if the cat is already on another antihistamine, adding Benadryl could cause sedation issues. 

Avoid gel capsules

Benadryl comes in tablet, gel capsule, and liquid form. Eddy cautions that gel capsules can sometimes contain a vehicle (i.e. the solvent used to carry the active ingredient) that can be toxic or irritating to cats. For this reason, he prefers tablet or liquid forms. 

Read the ingredient list

Some Benadryl products come with extra benefits, which means extra drugs. Be sure that diphenhydramine hydrochloride is the only active ingredient in the product you buy for your cat. Buying the generic version of Benadryl is fine.

Double check the dose

Because Benadryl is manufactured for creatures that weigh a lot more than cats, getting the dosage right can be tricky and often involves cutting a tablet into two. It's important not to overdose your cat, as this can result in seizures, breathing problems, and even death. For really small cats, it might be easier to get the correct dosage using liquid Benadryl.

Monitor for reactions

Unfortunately, it is possible for your cat to have an allergic reaction to the medicine he's taking to treat an allergic reaction, says Eddy. If you see signs like vomiting, diarrhea, lethargy, facial swelling, hives, or itchiness, call your veterinarian. And as mentioned above, it's also possible that your cat will become more hyper instead of more relaxed. 

What If My Itchy Cat Needs More Than Benadryl?

Keep in mind that even if a dose of Benadryl calms your cat's itchiness, it might not be treating the underlying problem. For example, if your cat has fleas or a fungal infection like ringworm, Benadryl will only offer temporary benefits. If your cat's itchiness doesn't go away, schedule a veterinary visit for your cat. Once your veterinarian is able to pinpoint the real cause of your cat's need to scratch, your pet will be on the road to long-lasting relief.