What Are The Potential Side Effects Of Deworming A Cat? (Useful Info)

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Every cat has to deal with worms at some point, but what happens when you start a deworming regimen? Let’s dive in and explore the potential side effects of deworming a cat as we discuss the best methods for keeping your feline friend healthy and free from pesky parasites.

Side Effects Of Cat Dewormer

Deworming a cat is an essential part of preventive healthcare to ensure the health and well-being of your pet. Many pet owners may purchase over-the-counter medications to treat conditions such as roundworms, hookworms, tapeworms, and other parasites that may inhabit a cat’s gastrointestinal tract.

While the overall risk of any significant side effects from using cat dewormers is low, it is always important to talk with your veterinarian about any potential risks when considering deworming your pet.

Common side effects you might observe in cats after deworming include lethargy and loss of appetite for a few days, as noted by Cornell University College Of Veterinary Medicine (CVM).

Some cats may also experience digestive upset, such as vomiting or diarrhea if they are sensitive or allergic to the medication prescribed by your veterinarian.

More severe complications, including digestive tract blockage, can occur in rare cases if giant worms are present before treatment. It does not pass through the cat’s system quickly enough after administering medication, and this is especially true in kittens whose intestinal tracts are smaller than their adult counterparts.

If vomiting or diarrhea occurs, it’s always best to consult your vet immediately, as some infections may warrant additional treatments.

Overall, deworming cats is necessary for preventive healthcare and disease management to reduce risk factors associated with parasites in cats’ intestines.

Talk with your veterinarian before deciding whether or not this procedure is necessary for your pet, and remember that no medication should be administered without supervision from a clientele care team member.

Sensitive Stomach

While deworming your cat is essential to keeping them healthy, it can also cause unwanted side effects. One common issue is a sensitive stomach that may lead to vomiting or diarrhea after treatment.

Cats are particularly prone to side effects from deworming because they have very delicate digestive systems. Stress, poor diet, parasites, or medications like antibiotics or vaccinations may further weaken the lining of the stomach and intestine, making them more susceptible to upset from deworming drugs.

If your cat has vomited or had diarrhea after taking a dewormer, you may need to try another prescription or ask your vet for advice on how else to proceed.

There are different medication classes in the form of pills, liquids, and injections, which can affect cats differently. Choosing the right one for your pet is essential in avoiding adverse reactions that could make your cat uncomfortable.

Adding probiotics to their diet can also help to restore balance and calm their sensitive stomach before and after taking medication. If their vomiting persists despite these changes, they should see a veterinarian as soon as possible to find out if any underlying medical problem is causing it.

Persistent vomiting could be an indication of an infection or parasite that should be addressed right away by a professional, so it doesn’t get worse over time and affect their health further down the road.

deworming a cat

Increased Salivation

One side effect may be increased salivation when a cat is put on a deworming medication. In most cases, increased salivation is just an immediate reaction to the taste of the medicine. It can cause visible drooling and requires no intervention; however, it should still be monitored by a veterinary professional for any rare or extreme reactions.

If your cat’s salivation does not dissipate within 1-2 hours of taking the medication, it may indicate a more severe reaction and should be discussed with your veterinarian immediately. Other signs of an allergic or adverse reaction may include spasms, vomiting, severe itching, difficulty breathing, and wheezing.

It is important to note that while increased salivation can be a side effect of deworming medication in cats, it generally poses no harm to the animal and will usually subside without any medical treatment required.

Contact your local veterinarian for medical advice and support if you have concerns about your cat’s health during or after a worming treatment.


Diarrhea is a common side effect of deworming a cat. Diarrhea occurs when the intestines are inflamed due to parasites or bacteria. Worms, such as roundworms and tapeworms, can migrate from the small intestine to other parts of the digestive tract and cause severe irritation.

Deworming medication is designed to break down worms to rid your cat of them and reduce inflammation in the digestive tract.

The most common symptoms of diarrhea in cats include frequent and watery stools, blood or mucus in seats, weight loss, dehydration due to loss of fluids, lethargy or fatigue, and vomiting.

In some cases, a cat may also experience abdominal pain or discomfort. These signs require immediate medical attention.

If your cat has been diagnosed with worms after your veterinarian has examined a stool sample, they may recommend deworming medication as part of your treatment plan for worm removal.

While this medication can effectively eliminate parasites from cats’ systems, side effects must be considered before beginning treatment, including diarrhea.

Before you start any deworming regimen, you must speak with your veterinarian about any potential risks associated with the type of medication used.

Loss/Lack Of Appetite

Loss or lack of appetite is a common side effect most cats experience after taking a worming hospital. This varies from cat to cat and usually doesn’t last long. However, it can take up to a week for them to return to their eating habits.

The most important thing you can do if your cat does not want to eat post-deworming is to ensure food and water intake and observe any additional signs of distress, such as lethargy or vomiting.

If your cat has not resumed everyday eating habits after the first week, consult your vet for further advice.

In some cases, it may be necessary for your vet to administer additional treatments or even re-administer the deworm treatment depending on the type of worming product used and the severity and duration of symptoms.

In addition to anorexia, other rarer side effects experienced by cats post-deworming include vomiting and diarrhea, as well as an overall reduction in appetite.

Allergic reactions are also possible but considered more irregular, so if you notice any severe side effects such as breathing difficulty, facial swelling, or fever, contact your vet immediately.

How Long Do Deworming Side Effects Last?

When cats are given deworming medicine, it is only natural to be concerned about possible side effects. Although adverse reactions of this kind are relatively rare, it pays to be aware of them so that you can take appropriate steps should something happen.

Unlike other drugs for cats, deworming medications rarely have any lasting side effects or impact on the pet’s health. The primary issue with administering dewormer is the possibility that the pet may experience gastrointestinal distress.

This could include vomiting, diarrhea, and lack of appetite, though this will typically subside once the body has time to adjust to its new chemistry after taking the medication.

In terms of duration, initial side effects can last anywhere from a few hours up to a couple of days in some cases. It is important to remember that each cat will react differently based on its physiology and other factors that may affect absorption and usage by its body.

Additionally, since several types of larvae are present in each species’ body at different development stages, some deworming rounds require multiple treatments over two to three weeks before full effectiveness is achieved.

During this period, occasional minor disturbances should not be considered cause for alarm. They will reduce naturally over time as long as proper care is taken regarding diet and lifestyle modifications that support digestive health, such as feeding a low-fat diet and limiting access to questionable food sources outdoors (i.e., mice).

Do Cats Poop Out Worms After Being Dewormed?

The short answer is no. Cats do not typically poop out worms after being dewormed. Although cats can carry a variety of worms, including roundworms, tapeworms, hookworms, and whipworms, this is not usually seen in the feces. In most cases, these parasites shed eggs that can be seen under microscopic examination of the stool.

Cats who test positive for worms and are put on medication show a reduced worm burden when rechecked. However, it is not common to see visible evidence of parasites being passed through the feces after deworming.

It may cause owners to doubt the effectiveness of their chosen dewormer, but the active ingredients in most oral treatments target migrating immature stages that are too small to be seen with the naked eye.

While not seeing signs of parasites while cleaning up stool is typical and expected after deworming a cat. It is essential to follow up with your veterinarian to ensure all stages of the worm parasite have been successfully killed by continuing treatments as directed or with multiple doses depending upon your pet’s health status and type of infestation.

Your vet may also need to collect additional fecal samples to assess whether any trace amounts of eggs remain to indicate further treatment or monitoring may be needed.

Do Cats Get Diarrhea After Deworming?

Cats can get diarrhea after being dewormed due to the medications used. A cat consuming an antiparasitic product may experience gastrointestinal distress resulting in loose stools or diarrhea.

Another frequent side effect of deworming is vomiting. Some cats experience digestive upset as their body expels the parasites from their system. Vomiting can be severe or mild in cases and usually leads to dehydration in cats if left untreated for too long, which can cause further complications.

Though it’s normal for cats to experience some discomfort with deworming, a few symptoms indicate your cat could be ill or developing an allergy or intolerance to the medication used for deworming your cat.

If your cat experiences any of these, it’s essential to seek veterinary attention immediately: lethargy, loss of appetite, fever, and pale gums (an indication of blood loss).

In most cases, however, cats tolerate deworming very well, and any symptoms will resolve once the medication has been eliminated from their system.

Be sure to provide plenty of fresh water and easily digestible food such as canned pumpkin (without spices), boiled chicken breasts, and cooked white rice while recovering from deworming treatment.

Monitor your kitty closely after deworming treatments and contact your veterinarian if any worrying symptoms persist beyond 24 hours following the treatment.

cat poops

Can I Feed My Cat After Deworming?

Deworming a cat is integral to keeping them healthy, but some side effects can unfortunately occur. One of the most common questions about deworming is whether feeding your cat right after the treatment is safe. The answer is yes, but you should consider some important points before doing so.

First, consult your veterinarian on what type of food they recommend after your pet’s deworming. While it’s safe to feed your cat soon after the process, they may advise you to wait a few hours until the medication has had enough time to take effect to minimize stomach upset or vomiting fully.

As long as you follow their instructions and monitor your feline friend for any health issues that may arise, then it should be okay to feed them as soon as they are dewormed.

It’s best practice, however, not to refrain from offering anything too heavy or rich following deworming – stick with something lighter such as boiled chicken or mashed potatoes. It’s also best to keep things on the smaller side (1 meal per day) to not overwhelm their digestive system and give them ample time to recover before feeding more food again.

Finally, plenty of fresh water should always be available for drinking throughout and post-deworming period. So dehydration does not occur, which can sometimes happen if cats do not eat enough food during this process due to illness or drug side effects.


In conclusion, the side effects of deworming a cat are typically minimal, with the most common being temporarily increased appetite and temporary changes in feces consistency and odor.

But it’s important to realize that while treatment is not always necessary, it can be life-saving if left untreated. In this case, the risks of treatment are far lower than the risks of an untreated infestation.

Your veterinarian will be able to advise you on the best way to proceed with your cat’s deworming care and should closely monitor any changes in his health or behavior during the time he is receiving medication for intestinal parasites or worms.

With appropriate care for both diagnosis and treatment, your cat can live a long and happy life free from these pesky parasites.

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