The Side Effects of Deworming a Puppy

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You are naturally concerned when your puppy has worms, but it's common and easy to treat.

The reason worms are a concern in puppies is because worms are intestinal parasites that rob puppies of important nutrients. Because a puppy's body is so small, a lack of nutrients can cause her to become quite ill in a short time if she goes untreated. The most common puppy parasites are roundworms, which are usually transmitted from the mother. Deworming side effects in puppies are usually short-lived and temporary.


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When to deworm puppies

Mother dogs with worms can pass on the worms to their puppies before they are even born, so young puppies are often treated for worms. Most of the time, says Purina, puppies are dewormed at 2, 4, 6, 8 and 12 weeks of age. Once your puppy reaches 12 weeks, you can continue to treat your puppy every three months for life with an effective dewormer. Mother dogs with puppies expected or on the way can be treated with dewormer during mating and before the birth of the puppies.

Deworming side effects in puppies

There are different types of worms, and as such, there are a few different treatment types. Deworming medication is frequently in the form of a tablet for adult dogs, but because puppies can have a hard time swallowing tablets, puppy dewormer is often in liquid form. According to Canine Weekly, deworming side effects in puppies can be a little disturbing because you can often see the worms leaving your puppy's body in the feces.


Symptoms of deworming puppies include minor intestinal issues such as diarrhea, but this should pass within a few days. Some behavior changes may be noticeable as your puppy's body passes the worms. If you see your puppy sick after worming, look for serious side effects such as blood in his stool, diarrhea that lasts longer than three days, vomiting, or other signs that your puppy is having an adverse reaction.

Puppy vomiting after deworming

With puppy worming tablets, side effects can include vomiting. According to Advantage Petcare, this is more likely if your puppy has a large amount of worms. If you administer a tablet, make sure your dog completely swallows it. Some dogs may try to spit out the tablet even several minutes later.


Deworming side effects are similar in full-grown dogs. The main difference is that a mature body is better able to handle the potential side effects of deworming medicine, so side effects may not be as noticeable or as serious in a mature dog. The best way to avoid the chance of side effects is to make sure you administer the proper dosage of medication.

Puppy drooling after deworming

VCA Hospitals says you may notice your puppy drooling after deworming if she receives a dose of a medication known as fenbendazole, which is in the brand names Panacur and Safe-Guard. Fenbendazole is used to treat a variety of parasites. At normal doses, you shouldn't notice anything amiss, but you might notice signs of an allergic reaction such as facial swelling, itchiness, hives, diarrhea, seizures, or shock. If this happens, seek veterinary care immediately. Fenbendazole can also cause excess salivation and vomiting.


Dogs, Cats, Pets lists a few possible dog behaviors after deworming. These include an upset stomach, lack of energy, or poor appetite. Sometimes, an upset stomach is a sign that the medication is working. You may even see signs of worms in the vomit; this means the medication is working to expel the parasites. Lack of energy should end after 24 hours or so. Likewise, the poor appetite should not last very long either.

Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.