What to expect when you worm a puppy for the first time

What to expect when you worm a puppy for the first time

Health & Safety

Young puppies grow and develop quickly, gaining weight and condition measurably on a daily basis during some points of their development, and the first year of a pup’s life is a very formative time for them in terms of both their physical and emotional development. If a puppy has worms, this can have an impact on the progress of their development as the worms rid the body of vital nutrients your pup needs to grow and thrive, which can lead to a loss of condition and weight and that can also make your puppy quite sick.

Puppies can also pick up worms very easily, even before they leave their dam and go outside for the first time. Pups can contract worms from their dam herself or other dogs that they live with, and when your pup is able to go outside for the first time, the number of places and ways in which your pup might pick up worms increase exponentially.

This means that sometimes, even young puppies will need to be wormed to safeguard them and ensure that they grow and thrive, and worming is generally a straightforward procedure that won’t cause the pup any problems, and that is perfectly safe.

However, there are some side effects that can accompany worming a dog, particularly a very young one or one that is being wormed for the first time. In this article we will explain some of the side effects you should potentially expect when you worm your puppy for the first time. Read on to learn more.

Picking the right wormer

First of all, it is vitally important to choose the right type of wormer for a young puppy, and to give the right dosage and administer it in the right way. This is true for adult dogs as well, but there is a smaller margin for error when it comes to worming a young pup, and they are likely to be more sensitive to the wormer itself and slightly more prone to displaying potential side effects after worming.

You should talk to your vet about the most appropriate type of wormer to use for your puppy, and have your vet prescribe the right dosage based on your pup’s weight and age. Your vet might also give your pup the wormer for you, or if not, they will provide advice on how to administer the medication at home.

Next, we’ll look at some of the most common side effects that can accompany worming a puppy for the first time.

Sickness and diarrhoea

Worms set up home in a dog’s stomach and intestines, latching onto the walls of the organs and draining essential nutrients from your dog’s body. Wormers of all types are designed to kill and eliminate worms of various specific types, and you may need different products for different types of worms. Again, your vet will advise you on what type of worms your pup is likely to have and provide the right product to eradicate them.

Digestive upsets after worming (usually within the first 24 hours) are fairly common in puppies as the wormer gets to work, and this may manifest as nausea and vomiting, and/or diarrhoea.

Be prepared for this and be vigilant about letting your pup out to go to the toilet whenever they need to, in order to avoid accidents in the home.

Additionally, if your pup does vomit after having their wormer, note how long after administering the wormer this happens. If your dog vomits too soon they might vomit all or some of the wormer itself back up, which may mean the need for a repeat dosage, potentially with a different product to try to avoid nausea with the next dose.

However, you should check on this with your vet, and don’t give your pup a second dose of any wormer after vomiting unless your vet recommends this.


Some pups might slobber or salivate more than normal after they’ve been wormed, which is another common and transient side effect of worming for some dogs, particularly young puppies. If your dog drools a lot or is quite slobbery anyway, you might not notice this, but it is something to bear in mind.

Again, hypersalivation will tend to occur (if it is going to) within 24 hours of worming, usually after a few hours. It can also be a precursor to vomiting, so bear this in mind if your pup starts looking as if they’re about to bring something up!

Generalised symptoms

Your pup may be a little quieter and less lively than normal for a while whilst the wormer starts to work, and they may also go off their food for a short while too. Drinking a little more water than usual is common as well, particularly if your dog is hypersalivating.

Bad reactions and more serious side effects

Acute or very serious reactions to wormers aren’t common even in young pups, assuming that you have given a safe, appropriate veterinary recommended product at the right dosage. However, some puppies may be allergic to certain wormers and react badly to them, and it is especially important to keep a look out for the signs of problems the first time the pup is wormed.

If your pup appears incredibly lethargic or if they display signs of being harder than normal to wake after worming, contact your vet as a matter of urgency. In rare and extreme cases, a bad reaction to a wormer can result in seizures and potentially loss of consciousness, which is an emergency that your vet needs to be informed of right away.



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