Many people believe that only the pets that walk outdoors can suffer from parasites, but this is just a popular misconception. Most domestic cats get affected with parasites at some point in their life. The good news is that modern deworming remedies allow to get rid of parasites. The bad news is that sometimes these dewormers cause side effects. Are cat dewormer side effects a reason for being concerned? Let’s try to find out the answer.

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Table of Contents:

Parasites in Cats and Their Types
Types of Cat Dewormer Side Effects
Frequently Asked Questions

Parasites in Cats and Their Types

Parasites are living organisms residing in the organisms of other creatures or on the top of their bodies. They live at the expense of their hosts, depriving them of valuable nutrients and making them suffer. There are two major groups of parasites that affect domestic cats:

  1. Insects (ectoparasites or ectozoons) are external parasites living on the skin. The most common of them are fleas.
  2. Worms (endoparasites or entozoons) are internal parasites that inhabit the inner organs – the digestive system, the heart, the lungs, etc.

Getting rid of worms is more difficult for several reasons. Firstly, you don’t see them, so you may be unaware of the infection. Secondly, various types of worms require various dewormers. The following types of worms choose cats as their hosts:

  • tapeworms;
  • roundworms;
  • hookworms;
  • whipworms;
  • heartworms;
  • pinworms.

Cats can catch worms in multiple ways even if they don’t walk outdoors. Various insects, such as fleas, mosquitoes, and flies often act as carriers. You can carry worms’ eggs on your shoes. Outdoor felines usually get wormy through the touching of other pets’ feces or infected soil. Sometimes, the symptoms of parasitic infections are prominent, but sometimes there are no noticeable symptoms. That is why experts recommend to deworm cats at least once a year just as a precaution. The common systems of a worm infection are the following:

  • vomiting, nausea, diarrhea;
  • abnormal weight loss;
  • unhealthy, flocky hair;
  • uncommonly low or high appetite;
  • a distended abdomen;
  • visible white segments resembling rice in the feces.

If you suspect a parasitic infection, go to the vet. The specialist will help to specify the type of worms and prescribe the treatment. Probably, you’ll have to make a feces analysis on helminth eggs. After that, use the appropriate dewormer to get rid of the parasites.

Types of Cat Dewormer Side Effects

It is generally accepted that no medication is 100% harmless. Cat dewormers sometimes cause side effects, like any other remedies. Usually, they don’t require any special treatment.

Increased Salivation

Froth at the mouth looks alarming, but in fact, there is nothing to worry about. An increased salivation is a physiological reaction to the unpleasant or unfamiliar taste of the drug or even its smell (cats are sharp-nosed.) You can give your cat some pure water or try to rinse its mouth using a syringe. Normally, this symptom quickly goes on its own.

Vomiting and Nausea

Vomiting after taking in a deworming remedy can occur in the case of severe infestation. Usually, it occurs not immediately but in 30-60 minutes after swallowing the drug. In this case, there’s no need to give another deworming pill right now. But it’s recommended to repeat the procedure in 7-10 days. If your cat vomits immediately after taking a pill, consult a vet – maybe, it makes sense to try another dewormer.


Diarrhea is a normal physiological reaction to deworming. Sometimes, dead or paralyzed worms are expelled with feces. Diarrhea can last 1-2 days; after that, don’t forget to sanitize the litterbox and the floor around it.
Sometimes (very rarely) cat dewormers cause severe side effects – convulsions, non-stop vomiting, intoxication or dehydration. The reasons are either overdosing or the idiosyncrasy. In these cases, you must consult a vet as soon as possible.

Frequently Asked Questions

Despite occasional side effects, deworming is mandatory for all domestic cats. Always keep in mind that worms cause much more harm to a cat than a deworming tablet. Let’s sum it up once again.

Q: How Long Do Dewormer Side Effects Last in Cats

A: Normally, if the cat is overall healthy, all side effects are gone within 24-48 hours. In sick, elderly or weak pets they can last some longer. If your kitty has a decreased appetite for some days after deworming, it’s ok. If the side effects are severe or last too long, consult a specialist.

Q: What Happens If You Give a Cat Too Much Dewormer?

A: It depends on the type of the dewormer, but that’s not good anyway, as your cat can get intoxication. In the case of overdosing, it’s recommended to take the pet to the vet immediately.

Q: How Long After Deworming a Cat Are the Worms Gone?

A: Most dewormers start working within 24 hours. The maximum effect is reached in 48-72 hours. The effect is preserved for 3-4 months, after which it’s recommended to repeat the procedure.

Q: How Often Should Cats Be Dewormed?

A: Healthy adult cats should be dewormed once a year as a precaution. For outdoor cats, deworming 4 times a year (once in 3 months) can be acceptable. If you are not sure whether your cat needs deworming right now or not, make a fecal test.


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Najma siddiqua

Can I deworm a cat who is sick from past 5 days and not eating properly and is weak?


If my cat had side effects like loss of appetite, weakness and diarrhea after the deworming med. What can I feed him?

Last edited 1 год назад by Sammy
Wayne oneal
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I have no question as your article on cat worming was very informative and it answered all my thoughts. I meant to give you a 5 star rating however I touched my screen wrong! Thankyou so much! 😊

Diane Wynne

My cat has had a small amount of hair loss from the site how long will it last and do I need a vet to see her she is showing no other signs but it has gone a bit sore looking

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