Worm medicine can cause side effects in dogs. Among them, we can observe a picture of hairy diarrhea after deworming. The causes can be varied and can involve either the parasites themselves causing the infection or the antiparasitic drug prescribed to prevent or treat the infectious disease. In any case, it is important to pay attention to the presence of this clinical sign and report it to the veterinary professional who prescribed the treatment, especially if it worsens or lasts for a long time.

If you want to find out How long does dog diarrhea last after taking worm medicine? , continue reading this AnimalWised article.

Why you gave the dog worm medicine

In order to understand the reasons for diarrhea in dogs after taking worm medicine, it is essential to be clear about the reason for which the medicine was administered, as side effects are common. Therefore, before addressing this question, it is important to point out that antiparasitic drugs can be administered for two different reasons:

  • Prevention of a parasitic disease
  • Treatment of a parasitic disease

Next, we will explain when to deworm a dog for each of these two goals.


Parasitic diseases must be prevented through two strategies:

  • Control measures : for example, not providing raw food to dogs, providing them with clean and potable water, preventing them from having access to rodents, game animals, dead animals, etc.
  • Routine deworming : consists of administering antiparasitic drugs on a regular basis in order to prevent the onset of a parasitic disease.

The frequency with which preventive deworming should be carried out can vary depending on multiple factors, the most important of which are:

  • The epidemiological characteristics of the area : the puppies will be exposed to a different level of risk depending on the prevalence of different parasitic diseases in the geographical area where they live.
  • The individual characteristics of each dog : the activity they carry out (hunting dogs, sheepdogs, etc.) and their diet (consumption of raw meat or offal) is particularly important.

Depending on the different factors that affect the risk of each animal, an appropriate deworming program must be implemented, which must always be designed and prescribed by a veterinary professional. In that regard:

  • Dogs that live indoors or in an apartment or that have limited access to the outside do not have direct contact with other dogs, nor do they have access to other risk factors (parks, children’s litter boxes, rodents, prey, corpses or viscera, snails or slugs, or raw meat) are considered low risk animals , which makes it sufficient to give worm medicine 1-2 times a year , or to perform routine coprological examinations and only deworm when the results are positive.
  • Dogs with access to the outside, to litter boxes, and in direct contact with other dogs , but which do not have access to other risk factors (rodents, prey, corpses or viscera, snails or slugs, or raw meat) are considered animals. medium risk , which should be dewormed 4 times a year , or else perform routine coprological exams and only deworm when the results are positive.
  • Dogs with access to the outside, to sand parks, and in direct contact with other dogs and with other risk factors (rodents, prey, corpses or viscera, snails or slugs, or raw meat) are considered high-risk animals , which must be dewormed 4 to 12 times a year .

There are few parasitic diseases that are solely related to the age of the animal. The risk of infection is present from birth, and therefore preventive deworming must be carried out throughout life. In fact, it should start at 2 weeks of life and repeat itself every fifteen days until it is 8 weeks old. From then on, deworming must be maintained at the frequency established depending on the risk, as explained above. 

Parasitic disease treatment

When preventive measures fail, and the animal catches a parasite, it is necessary to institute a specific antiparasitic treatment to deal with the causal agent of the disease.

Specific antiparasitic treatment must be initiated when the parasite species responsible for the infection is determined, and must be repeated depending on the period of permanence of the parasite species in question.

Causes for a dog with diarrhea after deworming

It is relatively frequent that, after deworming, tutors ask themselves: « why does the dog have diarrhea after taking worm medicine? ». Well, there are several causes that can explain this side effect in the dog:

  • The parasitic disease itself : many of the intestinal parasites cause diarrhea due to the cytotoxic effects and the mechanical action that the parasites exert on the intestinal mucosa. Despite the introduction of an antiparasitic treatment, it is possible for diarrhea to persist for the first few days, until all the parasites have died and the intestinal mucosa has regenerated.
  • Side effects after deworming a dog : Some antiparasitic drugs, such as bunamidine, can produce diarrhea as a side effect.
  • Error in dosage : Excessive dosage of a dewormer can exacerbate its side effects and produce, among other things, diarrhea.

As you can see, if the reason for deworming was to treat the parasitic disease, most likely this is the reason for the diarrhea, and this will also mark its duration, as we will see in the next topic

How long should the dewormer take effect and stop diarrhea in the dog?

The duration of deworming diarrhea in puppies will depend on the reason for which the antiparasitic drug was administered.

In the event that the diarrhea is due to the pathogenic effect of the parasitic agent itself, it is possible that it extends during the first days of the antiparasitic treatment . However, if the diarrhea is very profuse, or if it lasts for more than 7-10 days , it is important to go to a veterinarian , as in these cases the animal may become dehydrated and need fluid therapy.

In case you suspect that it is a side effect of the worm medicine , it is important to communicate this to the veterinarian or veterinarian who prescribed the treatment. If it is mild diarrhea, it is likely that the professional will decide to keep the same medication until the treatment is completed, even if the animal has less formed stools than normal during this time. In the case of severe diarrhea, it will be necessary to withdraw the treatment and use another active ingredient.

What to do if my dog ​​has diarrhea after deworming?

If the puppy, adult or elderly dog’s diarrhea is due to a pathogenic agent, you must wait for the treatment to fulfill its function so that the diarrhea stops. As we mentioned before, if it lasts for more than 7 days, then yes, you should consult a vet who will tell you what to do.

If it is a side effect of the dewormer, diarrhea should stop on its own after 24-48 hours. However, if it persists beyond that time, it will also be necessary to go to the veterinary center.

On the other hand, you can establish a bland diet or offer an easy-to-eat food to promote intestinal transit and not worsen the dog’s condition.

  • European Scientific Counsel Companion Animal Parasites (ESCCAP). (2021). Control of worms in dogs and cats . Guide nº01
  • European Scientific Counsel Companion Animal Parasites (ESCCAP). (2013). Control of intestinal protozoa in dogs and cats. Guide nº06


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