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Help, my dog is sick after deworming, what should I do? As with many stressful things in life, dealing with a sick dog is something that may trigger feeling of helplessness and despair. Veterinarian Dr. Ivana Crnec shares several potential causes and what to do if your dog is sick after deworming.

A Word About Deworming Products For Dogs 

There is a wide variety of worms that can affect dogs. They thrive inside the dog’s intestines where they have a readily available food source and relatively safe from the dog’s immune defenses. Some are fairly benign while others cause life-threatening conditions. That is why it is important to have your dog regularly dewormed.

Deworming products are usually given orally, in the form of a chewable treat or pill. Rarely, some deworming products can be applied topically in the form of a spot-on treatment or in the form of an injectable liquid administered under the skin,

Different wormers have different active ingredients, and that is why it is important to learn how each of them acts. Most deworming products contain two or three different active ingredients. Here are the five most frequently seen anti-worms drugs for dogs.

Pyrantel Pamoate

Pyrantel pamoate is a particularly safe, yet effective deworming ingredient that is powerful against roundworms, hookworms and pinworms. To get rid of all worm stages, the dose of pyrantel pamoate must be repeated two or three times, with 2 to 4 weeks pauses between doses.

Pyrantel pamoate acts by paralyzing the worms attached to the intestinal lining. Once paralyzed, the worms can easily be eliminated through the dogs' feces. In the outside environment, the eliminated worms stay alive for a short period of time.


Piperazine is effective only against two roundworm types, and to achieve full efficacy, it should be administered a minimum of two times, 10 to 14 days apart. Because of its limited effectiveness, piperazine is rarely used on its own – more often it is combined with other wormers.


Fenbendazole is classified as a broad-spectrum dewormer. The term broad-spectrum means it is effective against several different worm types, including roundworms, whipworms, hookworms and giardia. Fenbendazole is administered once per day for three days in a row.

Fenbendazole acts by decreasing the worms’ energy reserves and interrupting their ability to eliminate waste.


Praziquantel is the dewormer of choice for treating dogs with adult tapeworm infections. Since, praziquantel does not destroy the tapeworm eggs, re-infestations are likely to occur. That is why vets recommend giving deworming treatments on a regular basis.

Normally, the tapeworms are resistant to intestinal juices. Praziquantel acts by disrupting that resistance which causes the tapeworms to be disintegrated and finally, absorbed into the dog’s body.


Ivermectin is the preventative of choice against heartworms. Additionally, ivermectin is effective against several external parasites, such as mange, lice and ear mites.

It is important to emphasize that ivermectin kills only the parasites that infected the dog in the previous month. That is why ivermectin should be used all year round. Ivermectin acts by disabling the heartworm larva’s central nervous system.

Finally, it must be well-noted that ivermectin must not be used in dogs with the MDR1 gene issue, because they show higher sensitivities to this drugs. Such breeds include Collies, Shelties and mixes containing one of these breeds in their ancestry lineage. 

Help, My Dog is Sick After Deworming

There are some common side-effects of deworming products that dog owners should be aware of. 

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Here's the thing: deworming products are specifically designed to target the worms while sparing the dog. 

However, in some rare circumstances, more sensitive dogs can experience several side-effects. These are the most commonly reported side-effects of deworming treatments.

Lack of appetite

Shortly after the deworming treatment is applied, it is reasonable to expect a slightly decreased, or in more extreme cases, a complete loss of appetite. 

This side effect is temporary and usually subsides in the following 24 to 48 hours. After that timeframe, most dogs regain their normal appetites and continue as if nothing happened.

If your dog’s appetite does not return to normal, two days after the deworming treatment, call your trusted vet and schedule an appointment.

Diarrhea and/or vomiting

After receiving a deworming treatment, it is not unusual for dogs to develop diarrhea which usually lasts for about a day or two. The dog can either produce normal poops, but defecates too frequently or he or she may produce watery, shapeless droppings.

Vomiting is another common yet benign side-effect. Same as the diarrhea, the vomiting is expected to subside in a day or two. 

If either the vomiting or the diarrhea persists for longer than two days post-treatments, do not hesitate to talk to your vet.

Sluggish mood

After giving deworming products to dogs, dogs may feel a bit under the weather. This is more striking in otherwise hyperactive dogs that race around the house all the time.

 Same as the previously described side-effects, the sluggish mood should not last for more than two days. If it has been more than 48 hours since the treatment and your dog is still feeling blue, have your vet check the dog. 

How can I care for my dog after receiving deworming treatment?

Caring for a dog after its deworming treatments is pretty straightforward. Here is what you need to do:

  •  Avoid vigorous training and overexertion. In most cases a slow-paced walk around the block is enough is enough for the first day or two after treatment.
  • Never force-feed your dog if vomiting or lacking appetite. Going a day or two is less harmful than force feeding and provoking a more serious digestive upset. If you want to help, just give your dog a high-quality probiotic formulated specifically for dogs.
  •  Love your dog immensely and lavish him/her with plenty of affection and attention. Dogs are very sensitive and our support means the world to them.

Concluding Thoughts

Regular and adequate deworming treatments are necessary for preventing worm-related health issues. Although sometimes, the deworming treatments can have certain side-effects, they are rare, benign and usually self-limiting. Plus, the risk of side-effects, as a con is definitely outweighed by the pros of using deworming treatments.

About The Author

Dr. Ivana Crnec is a graduate of the University Sv. Kliment Ohridski’s Faculty of Veterinary Medicine in Bitola, Republic of Macedonia.

Finally, if any of the side-effects persists for more than two days, which is extremely rare, make an appointment with your trusted vet. 


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