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4 Side Effects of Deworming a Puppy: What You Should Expect

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By Nicole Cosgrove

labrador puppy getting dewormed

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Reviewed & Fact-Checked By

Dr. Paola Cuevas

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Deworming a dog is an important task for any owner, but it’s essential for those of us that have puppies. Contracting worms is a real danger for a young pup. Worms are parasites, which means they attach themselves to the inside of your puppy and suck the nutrients from them. This means they are being starved of essential vitamins and minerals they need to develop strong bodies.

This can lead to stunted growth, illness, and even death if left untreated. So, as a responsible owner, you will need to treat your pup for worms. The problem is, as with any medication, there is always a chance of side effects. Although reactions to standard medications, such as deworming tablets, are rare, they can be severe if left untreated.

To help you understand if your pup has reacted to his deworming tablets, we have listed them below. This way, you can identify them quickly and make sure they are nothing to be overly concerned about.

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What Are Puppy Worms?

The most common puppy parasites are roundworms, tapeworms, hookworms, whipworms, and heartworms. Vets recommend deworming puppies for the first time at around 2–3 weeks old. Roundworms can be passed from the mother to the pup via the placenta and the milk they take from her.

Although different types of worms are harmful in different ways, the general description of a worm is that it is a parasite that will make your pup ill. Medication supplied by your vet will cause the parasites to die, hopefully without adverse effects on your pup.

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Top 4 Side Effects of Deworming a Puppy:

Here is a list of the most serious and common effects that worming tablets can have on your pup.

1. Diarrhea

Dog Diarrhea_shutterstock_A-photographyy
Image Credit: A-photographyy, shutterstock

The most common type of worms in pups is intestinal worms. They latch on to the intestine, where they will take nutrients from food as it passes through. Once the medication is given and the worms die, they will fill up the intestine causing the body to flush them through.

So, naturally, one of the most common side effects after deworming puppy dogs is diarrhea. His body will pass lots of feces to rid itself of the dead worms.

So be prepared to see them coming out in his poop or even on their own in large bundles of what looks like spaghetti if the infestation is large. Sorry for the food comparison, but it’s all par for the puppy course (or in this case, hopefully not!)

2. Vomiting

Dog vomit in the living room on the floor_cunaplus_shutterstock
Image Credit: Cunaplus, Shutterstock

Due to some of the drugs used in worming tablets, your pup can suffer from nausea immediately after being given the pill due to it reacting with his stomach acids. He may wretch to get rid of the tablet.

When not administered in tablet form, he may still experience nausea sometime after being given the meds. This is because the medication can cause irritation and inflammation of the stomach lining. This can cause the body to react and expel the medication by vomiting. Be sure to monitor your puppy when he is sick. Not only to keep him safe but also to see if the tablet has come back up. If it has, you’ll need to discuss with your vet regarding another round of deworming treatment.

Ensure he has access to clean, fresh water to replace any lost fluids he expels through vomiting.

3. Excessive Salivation

Drooling sleepy Irish Setter_Reddogs_shutterstock
Image Credit: Reddogs, Shutterstock

Whether your pup is a slobber monster or not, deworming tablets can cause him to drool excessively. This links into the same reasoning as vomiting. When your pup’s tummy is upset, he will drool as his stomach flips. Much like a human does when the saliva glands react to the feeling of nausea.

If your puppy already slobbers, you might notice that it becomes excessive after you have given him the deworming medication. This means he is losing fluids, leading to dehydration if not counteracted with an extra intake of water. Again, just make sure he always has access to water to drink when he needs to. The drooling will often subside after a couple of hours at most.

4. Lack of Appetite

Dog No Appetite_shutterstock_ Velimir Zeland
Image Credit: Velimir Zeland, shutterstock

If your puppy loses his appetite after being given the medication, it will be because of an upset stomach. Even if he isn’t getting sick or doesn’t have diarrhea, he can still have a sore or upset stomach. It naturally follows that if all of the parasites in the stomach or intestine die, the lining of the stomach wall and the intestines themselves will become inflamed.

Feeling sick will cause a lack of appetite. Don’t worry, though, lack of appetite is usually short-lived in most pups. Lasting, on average, a maximum of 24 hours.Divider 5

Extreme Side Effects of Deworming a Dog

If any of these side effects last for more than 24 hours, you will need to see your veterinarian for advice. Rare, extreme side effects to look for are acute lethargy, seizures, or coma. These are severe signs that your puppy has had a significant reaction to the medication and needs immediate medical attention.

If any of these or other unusual effects develop, take your puppy to the nearest vet or emergency pet hospital as quickly as possible. It is rare, but unfortunately, it does happen. And it’s better to be safe than sorry.

A Word of Caution

Deworming medication should always be prescribed by a veterinarian, especially the first time. Deworming a heavily infested puppy or a dog with heartworms should be done under medical supervision and may also require additional medical treatments.

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Although side effects are a real concern with deworming medication, they are usually short-lived, and extreme reactions are rare. Veterinarians advise, despite the potential side effects, that deworming medications are still the best prevention and solution for treating worms in puppies and adult dogs alike. They are regulated and scientifically tested to ensure their safety.

As a dog owner, you can rest assured that these preventative and reactive deworming products are beneficial for your pup’s health, not detrimental.

If in doubt, seek help from a qualified professional.

Featured Image Credit: Ilike, Shutterstock

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