How long will my puppy have diarrhea after deworming? Pet's info: Dog | Havanese | Male | unneutered | 3 months and 18 days old

You may not see any worms after a dose of a [dewormer](https://www.petcoach.co/article/fecal-exams-worming-schedules-for-dogs/), but if the diarrhea and lethargy continue, Kiba should be examined by a vet to determine the cause. He could have a parasite that is not susceptible to the dewormer that you used or he could have a viral infection. Your vet can test a stool sample to help diagnose the specific parasite present and then prescribe medications to treat the issue. If he has not been vaccinated against [parvovirus](https://www.petcoach.co/dog/condition/parvovirus/), then he should be examined by a vet and be tested for it, especially if he starts vomiting or you notice any blood in the diarrhea.

It's common for puppies to vomit dead worms or pass them in their stool after they have been dewormed - this indicates that the dewormer worked. She may also be a bit tired for a day or two after deworming. Normally, she should be acting normal again and any diarrhea should have resolved within 48 hours after deworming - so if it's been longer than this and she is still acting lethargic or having any other symptoms, I would recommend having her examined by a vet to be safe - she may have a more serious problem, such as parvo, that would require veterinary treatment.

Hello and welcome to Petco Pet Education Center, formerly Petcoach. I'm sorry that Lilly Ann isn't feeling well. Often when puppies have a 'high worm burden' meaning there are LOTS of worms, when the dewormer is given the massive die-off causes diarrhea and GI upset. A concern with worms in puppies is a condition called intussusception (where the one side of the intestine 'telescopes' into the other side). This is very serious and requires surgery to fix. Signs of this include weakness, abdominal pain, not eating, vomiting, and diarrhea. It can be very difficult to determine normal diarrhea and GI upset from this condition, as the signs of the worms moving through can be similar. I would suggest that if Lilly Ann's abdomen seems distended, painful, or if she won't eat anything (even treats) or is vomiting, then I would have her into your vet to check for this condition. It can be hard to diagnose and an ultrasound is often required, but your vet will first examine Lilly Ann and feel her belly to see if it feels normal or not. This condition can also 'slide' or come and go, making it more difficult. If this is just worms, Lilly Ann should get better quite quickly. A visit to the vet is always recommended just in case, as puppies can get very sick much more quickly than older dogs. Best of luck with Lilly Ann, I hope she feels better soon!

Sometimes, side effects of certain dewormers may cause stomach upset. Consider a short fast 8-12 hours followed by a bland diet fed in small, frequent amounts until symptoms resolve. Transition slowly to the regular diet afterwards. If she remains lethargic or if the stomach upset persists, have her seen by your veterinarian or at the nearest veterinary ER.

My puppy has diarrhea after deworming. Is that normal? How long?

Updated On September 23rd, 2025

Pet's info: Dog | Havanese | Male | unneutered | 3 months and 18 days old

How long will my puppy have diarrhea after deworming?

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5 Answers

Most Helpful Answer

Answered By Dr. Melanie, BVSc MS 102

Veterinarian

Published on September 12th, 2016

It is normal to see some diarrhea and little lethargy after giving a [deworming treatment](https://www.petcoach.co/article/deworming-your-dog-what-to-expect). You may or may not see worms in his diarrhea. The side effects of the diarrhea and lethargy should only last 24-48 hours after giving the worming treatment. If they continue longer than that, or if Kiba becomes lethargic or refuses to eat or drink, you should take him into your vet for an exam.

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My puppy has diarrhea after deworming. Is that normal? How long?

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