Cat Antihistamine Side Effects

A cat antihistamine is a drug that reduces the symptoms of allergic reactions in felines. It has no application in the treatment of any disease caused by a pathogen, because antihistamines are only useful for problems that are actually caused by the immune system, such as in an allergic reaction. Antihistamines are different from most other drugs in that they inhibit aspects of the immune system, whereas most medications strengthen the immune system. Antihistamines are available as both prescription medications and over the counter drugs. The kinds you can get over the counter are less potent and do not last as long as the prescription forms.

How Antihistamines Work

A state of being allergic to something is caused by an oversensitive immune system. The immune system in an allergic cat confuses harmless particles, such as pollen or dust, with dangerous organisms, such as harmful bacteria. In response to what it interprets as a threat, the cat's immune system releases chemicals called histamines into its blood stream. Histamines work well for combating infections, but only result in discomfort when applied to harmless particles. Antihistamines are a branch of synthetic chemicals that inhibit the release of histamines into the body, thereby lessening the effects of allergic reactions.

How to Tell if Your Cat Has Allergies

There are a huge number of different substances that your cat could be allergic to, and different allergens usually give rise to different symptoms, so there are a wide variety of symptoms your cat could display that may imply an allergy. Generally, people find out that their cat has an allergy when diarrhea, vomiting, itchy or irritated skin, or hair loss occurs shortly after the cat was exposed to a new substance. The veterinarian can test cats for specific allergies using a blood or skin sample.

Side Effects of Antihistamines

Each different antihistamine can give rise to different side effects, but the most common side effects experienced by cats are sedation, hyperactivity, dry mouth, lack of appetite, and problems with bowel movements. Antihistamines will usually not have any side effects on your cat if they are dosed and applied as recommended. Less exact doses will be more likely to yield negative side effects. Over the counter antihistamines commonly cause drowsiness in cats, but prescription antihistamines generally do not have this effect.


Antihistamines affect every individual organism differently, so it is important to carefully consider which kind of antihistamine is right for your pet. It is not recommended to administer antihistamines to your cat until you have talked to a veterinarian about the different antihistamines available and what the daily dosage should be.

If your cat suffers from allergies, you could relieve him of a lot of discomfort if you started to give it antihistamines. However, you must remember to research antihistamine doses for cats, or talk to your vet about the proper dosage to administer. The side effects of improperly administered antihistamines could be more uncomfortable for a cat than the allergy the antihistamines were originally administered to treat.