Can Deworming Cause Sickness in Cats?

Feeling punky because the dewormer was funky.

Feeling punky because the dewormer was funky.

Deworming is essential should your cat get harmful internal parasites. Dewormers are toxic chemicals, so side effects to these treatments can occur. They often manifest within 24 hours. Pet owners should be on the lookout for a variety of issues.

A Sensitive Stomach

There is a lot going on in your cat's stomach during the deworming process. Some cats vomit during deworming due to the strength of the medication combined with the parasites moving through its digestive system. If your cat vomits within an hour of taking the medication, you should seek veterinary care. Vomiting can cause dehydration, and your cat may need to be admitted to a veterinarian hospital for fluids and other treatments.

Loss of Appetite

Dewormer medications are strong. After all, the goal is to rid your cat of the parasites in its system. So it's not surprising that your feline friend can lose its appetite until the medication is through its system. This side effect is usually temporary and typically lasts only a few days. However, if your cat's appetite doesn't increase after more than three to four days, contact your veterinarian for help. Your cat may need medication to help it get going again.


After receiving deworming medications, it's common for cats to suffer from diarrhea. It's also common to find worms in cats' stool. You may notice bloody stool. These symptoms usually last for only two to three days. If the symptoms persist, your veterinarian may recommend other medications such as metronidazole or prednisone, which control inflammation associated with inflammatory bowel disease.

Increased Salivation

Increased salivation in cats after a deworming treatment is a common side effect, that, like others, usually lasts only two to three days. However, if you notice your cat is foaming at the mouth rather than salivating, contact your veterinarian immediately. Your cat could have more serious condition, such as rabies.

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