Petco Text Logo
Petco Pet Logo

  • Two Easy Ways to Start Earning Rewards!

    rewards header
    Become a member today!
    Members-only pricing and offers, personalized care notifications, Vital Care points back on every purchase and more!
    Already a member? Sign in
    Petco Pay LogoBecome a credit card member today!

    Earn 2X Pals Rewards points at Petco
    when you use Petco Pay!

    APPLY NOW
    Learn More About Petco Pay Benefits

My kitten is sick after deworming. Is it worms or another illness?

Updated on September 23rd, 2025

Pet's info: Cat | American Shorthair | Male | unneutered | 2 months and 6 days old

My 8 week kitten just had his first deworming 3 days ago but now he appears very sick. How can I tell if he has intestinal worms or something else?

5 Answers

Most Helpful Answer

Dr. Melanie, BVSc MS

Answered By Dr. Melanie, BVSc MS

Veterinarian

Published on September 7th, 2016

Poor Frodo! Some cats do vomit during deworming due to the strength of the medication combined with the parasites moving through the GI system. These side effects should only last a few days, so if it's been longer than that, I would be concerned that it could be due to something else, such as a GI illness, a foreign body, or pancreatitis. I recommend withholding food for 12 hours, then feeding a bland diet of boiled white meat chicken (no bones) in small amounts several times a day for a couple of days. Then slowly add back in his normal diet. If the vomiting continues in the absence of food, he vomits the bland diet, develops diarrhea, stops drinking water, starts vomiting water, or becomes very lethargic, he will need to see a vet right away.
Vote Icon17Pet Parents found this answer helpful

Related Answers from Veterinarians

  • Answered By Dr. Melanie, BVSc MS

    Veterinarian

    Published on February 19th, 2019

    Yes, this can be caused by the medication and subsequent killing of the worms. Keep an eye on this kitten, and if it becomes lethargic, anorexic, continues to vomit, or keeps having diarrhea, take it into a vet right away.

    Vote Icon

    1Pet Parents found this answer helpful

  • Answered By Janie von Waldburg, DVM

    Veterinarian

    Published on May 17th, 2015

    This is common. It may taste bad or you may have forced him to take it. Most likely you could give him another dose with some food but consult your vet first. I am more concerned about what type of worms he has and if you have had a fecal test performed.

    Vote Icon

    11Pet Parents found this answer helpful

  • Answered By Dr. Strydom, DVM

    Veterinarian

    Published on September 15th, 2019

    The cats need to see a vet. We cannot diagnose worms based on your description. I suggest you get the cats to a vet so you can get a proper diagnosis of what type of worms they are and then they can be properly treated. Over the counter dewormers do not treat for every possible type of worm a cat can have. You need the diagnosis so the appropriate dewormer can be given. If they are vomiting worms they have a high worm burden and the blood is very concerning.

    Vote Icon

    1Pet Parents found this answer helpful

  • Answered By Emily, DVM

    Veterinarian

    Published on June 1st, 2017

    Hello
    It is unusual for worms to cause vomiting in a cat Crowley's age. While most OTC dewormers are safe it may not solve his vomiting.
    Other considerations for vomiting include a foreign body, dietary indiscretion (eating something that doesn't agree with his system), liver disease, an infection and some other rarer diseases.
    If Crowley's vomiting continues or he has any signs of pain, decreased appetite, diarrhea or weakness he should be examined by a veterinarian to make sure nothing else is going b with him.

    Vote Icon

    1Pet Parents found this answer helpful

Smart Picks for Smart Questions

Health & Wellness
Why is my kitten vomiting yellow and not eating after dewormer?
Thank you for submitting your question regarding your kitten. If he is not improving, then I recommend that he has a further work up. He should have fecal testing, blood work and x-rays of his abdomen to determine the cause of his vomiting and inappetance. Kittens can react to deworming medication, but it is typically a short lived reaction. It worries me that he is still ill. There is likely another another disease process present. In the meantime, encourage him to drink so that he does not become dehydrated. I hope this information helps!
Updated on September 23rd, 2025
Health & Wellness
My kitten is throwing up after deworming medicine. What should I do?
Thank toy for submitting your question regarding Dusty. I would contact her veterinarian in the morning to let them know of the vomiting. It is likely due to the deworming medication. It can sometimes cause vomiting as the parasites are being killed. They may send her home with an anti-nausea medication if this is the case. This medication can typically given as an injection by the veterinarian and then tablets to continue at home. I hope this information helps!
Updated on September 23rd, 2025
Vet Q & A
Why is my kitten not eating and hunching after dewormer shot?
It is possible that the worms were the reason why he wasn't eating, and the deworming treatment itself can make him feel nauseous and unwell. It's the result of the dead worms moving through his GI system. I would recommend offering him a bland diet of boiled white meat chicken (no bones) in small amounts to try to tempt him to eat. You can also soak his dry food in tuna juice, or offer him gently warmed really smelly wet food, such as sardine or fish based. If he still isn't eating in the morning, I would have him seen by the vet again. It will take at least two deworming treatments to kill all the worms.
Updated on September 23rd, 2025
Health & Wellness
How long after deworming should my cat stop vomiting from worms?
Deworming doesn't directly stop vomiting. IF the vomiting is indeed caused by the intestinal worms, I would expect vomiting to stop within a week or so of deworming, but it could be longer if the parasite load was causing a lot of irritation. I would still recommend a recheck if still vomiting after 5-7 days.
Updated on September 23rd, 2025
Health & Wellness
My kitten vomited after deworming medicine. What should I do now?
If he vomited within 2 hours, I would recommend calling your vet to let them know and picking up a second dose to repeat the treatment. It likely didn't have enough time to absorb in to Allyson's system.
Updated on September 23rd, 2025
Health & Wellness
Why is my kitten spitting up & has loose gray poop after worm meds?
There are many causes of GI upset. It’s possibly it is related to the dewormer but other causes are also possible and the most common are other types of worms not killed by the medication, coccidia, giardia and bacterial over growth. If your kitten remains sick for longer than 24 hours, I recommend to have her examined by her veterinarian. Bring in a stool sample for testing. Young kittens are more fragile than adults so it’s best to play it safe. I hope she starts feeling better quickly and please feel free to post any additional questions.
Updated on September 23rd, 2025
Health & Wellness
Kitten threw up after dewormer or tuna. Should I call the vet?
The deworming treatment can make Happy vomit as a side effect, but the tuna could cause it too. If he's stopped vomiting, you don't have to take him into the vet but if he wakes up and starts vomiting again, he will need to see a vet.
Updated on September 23rd, 2025

Related Searches

Prescription Dewormer for CatsCat FoodDewormer Treatments for CatsCat SuppliesWet Cat FoodPrescription Dewormer for DogsHeartworm Prevention for CatsCat LaxativesCat MedicineElectrolytes for CatsAntifungal Medication for CatsDog Dewormers & Worm MedicineVaccines and Shots for CatsCanned Cat FoodCat Thyroid MedicationVeterinary Diet Cat FoodPrescription Flea & Tick Medicine for CatsKitten FoodCat Urinary Tract & Kidney MedicationCat Seizure Medication
Have A Vet Question?

Book an appointment with the pros – our expert vets are here to help.

Book Now

Share

Styled arrow button