What Should I Expect After Deworming My Dog?

By Betty Lewis

Disgusting as they are, worms aren't uncommon in dogs. They're transmitted through routine activities, such as grooming and nursing. In fact, many dogs are born with worms. Tapeworms, roundworms, hookworms and whipworms are commonly seen in dogs and, fortunately, are easy to treat. A dog’s reaction to deworming depends on the type of worms infesting the dog and the medication used to kill them.

Diagnosis Before Treatment

Signs of intestinal worms include diarrhea, vomiting, a swollen stomach and weight loss. If your dog shows any symptoms of parasitic infection, he should see the vet. The symptoms mimic those of a host of other potential illnesses. The vet will rely on a fecal sample for diagnosis and to determine the proper medication to treat the dog's worms.

Choosing a Dewormer

A variety of medications, such as fenbendazole and pyrantel, are available to eradicate canine worms. Your vet will recommend a dewormer based on your dog's age, his health and the type of worms he's infected with. A dog's reaction to deworming will vary according to the medication used and the worm that's being killed. It's not unusual for a dog to experience vomiting, diarrhea and worms in his stool after a dose of worming medication.



As a broad-spectrum dewormer, fenbendazole treats hookworms, whipworms, roundworms and one type of tapeworm, as well as the intestinal protozoan Giardia. A dog may experience nausea or vomiting after taking fenbendazole, which is usually administered for three to five consecutive days, depending on the parasite. If the infection is severe, the dog may require a second round of treatment three weeks later.

Pyrantel Pamoate

Pyrantel pamoate paralyzes roundworms and hookworms, causing the parasites to loosen their grip on the intestines and pass through the digestive system and die. Common side effects of pyrantel pamoate include straining during defecation, diarrhea and occasional vomiting. Be prepared to see living worms in your dog's feces, but take heart in knowing they will die because they cannot live outside their host. A vet will usually direct multiple doses a few weeks apart.


Used to treat roundworm, piperazine has effects similar to those of pyrantel: worms in the stool, diarrhea, nausea and vomiting. Vets give multiple administrations of piperazine about a dozen days apart.


An oral medication, epsiprantel is used for killing tapeworm in dogs. Potential side effects are rare and usually occur only when the medication is given in high dosages. A high dose of epsiprantel can cause vomiting and diarrhea.


Available in injectable, topical and tablet form, praziquantel disintegrates the parasite to be absorbed by your dog's body. If administered as a shot, your dog may scratch at his injection site; a few dogs experience nausea, vomiting and diarrhea.

Your vet has multiple medications to choose from for deworming a dog. Some medications work on one type of worm; others kill more than one parasite. Sometimes a vet will combine medications to tackle a variety of conditions.