Puppy Dewormer: Where to Find the Best Options and How it Works

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Treating puppies for worms is a universal practice among veterinarians, but why? Your little fluffy friend is so new and perfect! How could she possibly have worms? I mean, the word “de-worming” means that they have worms to begin with, right?

Believe it or not, most dogs get worms at some point during their lives, and puppies are the most likely to be infected. Worms are often just part of the package deal when you’re a dog parent. Young puppies can get worms from their mothers in utero and through breastfeeding. Older puppies and adult dogs pick up worms by doing their favorite things — slurping up muddy water, licking dirt off their paws, and chewing up dirty stuff they find outside.

Fortunately, screening and treating dogs for these internal parasites is a daily practice in every veterinary office. Knowing about treatment will help keep a routine veterinary issue from feeling like major life stress or a failure as a pet parent.

What you need to know about worms

The term “worms” includes several types of parasites that can affect the gut, heart, and other organs of dogs at any life stage (scroll down for a list). Puppies are extra vulnerable to parasitic infections for a couple of reasons: there are more ways that puppies can become infected, such as through breastmilk while nursing, and because their immune systems are still developing, puppies are not as able to fight off infection.

Most de-wormers are broad-spectrum, which means that they treat a variety of different types of parasites. But it’s important to know that no single de-wormer treats all species of parasites. If your puppy is diagnosed with worms, your vet can tell you what type of medication will be effective. Both prescription and over-the-counter medications are effective, but be sure that you know what worm you are treating and read the labels to find the right medication.

Please note: Heartworms are not covered here because there are no over-the-counter medications available for heartworms. If your dog is diagnosed with heartworm, it will be necessary to work closely with a veterinarian for weeks to months to treat the infection and reduce the risk of long-lasting health issues.

How serious are worms?

When it comes to worms, an infection can vary from quite minor to extremely serious, depending on the type of parasite and severity of the infection. It’s important to work with your vet to do scheduled screenings, get a clear diagnosis when an infection is found, and use the appropriate treatment. As you will see, there are many treatment options and the choices can be confusing.

Below, each type of worm, treatment options, and info on prevention is listed. For more information, check out the excellent online resources at The Companion Animal Parasite Council, including maps showing how common each type of parasite is, county by county in the US.

Puppy dewormers and how they work

Dewormers can be given as an oral medication or an injection. It is so common for puppies to be exposed to roundworm in utero or during nursing, most veterinarians use a standard de-worming treatment every two weeks starting at two weeks of age: ages 2, 3, 6, 8, 10 weeks. The treatment is repeated because the medicine kills worms, not eggs, so a series of treatments is needed to kill the worms as they hatch.


Roundworms live in the intestines of affected dogs and are the most common parasite found in puppies and adult dogs. This is because roundworms can be contracted in many different ways.

Puppies can get roundworms from:

  • their mother in utero through the placenta
  • after birth through breastmilk

Dogs can also be infected by:

  • eating infected feces
  • eating soil contaminated with feces
  • eating one of the “transport hosts” of roundworms: earthworms, cockroaches, and small mammals such as mice.

Symptoms of severe roundworm infection in dogs:

  • weight loss
  • diarrhea & vomiting
  • dull hair
  • cough
  • a swollen belly

Roundworms can also infect people, and if undetected can lead to organ damage and neurologic problems. People can get infected through contact with feces and soil that is contaminated with feces, so glove up or cover your hands with a plastic bag when you’re picking up after your dog.


Tapeworms live in the intestines of affected dogs. Most dogs don’t show symptoms of tapeworms, and infection is usually diagnosed when a person sees white, rice-grain size segments of the tapeworm around the dog’s anus, in their bedding, or in their feces.

(Personal note: To my great surprise, when my dog had tapeworms, I was able to see these rice-size segments moving on their own. Did I take a video to show the vet? Yes. But I’ll spare you the visual experience; it’s truly something I can never un-see.)

Dogs contract tapeworms by eating an animal that is an intermediate host of the tapeworm:

  • Fleas can carry the tapeworm Dipylidium caninum
  • Small rodents such as mice, rats, and squirrels, can carry Taenia and Echinococcus tapeworms

Flea control is a very important factor in avoiding tapeworm infection in dogs and cats.

Although it’s possible for people, particularly children, to become infected with Dipylidium tapeworms from dogs, such infections are uncommon, mild, and easily treated.


Hookworms live in the intestines of affected dogs. Hookworms can cause serious blood loss and are particularly dangerous for puppies.

Dogs can get hookworms by:

  • eating contaminated soil
  • licking contaminated dirt from their paws and coat
  • skin contact with hookworm larvae in soil, which can penetrate skin

Hookworms can also infect people, particularly by contact with soil that has active worm larvae. Hookworms are easily treated in people, but can cause mild to severe discomfort.


Whipworms live in the intestines of affected dogs, where the large and small intestines meet.

Dogs contract whipworms by:

  • eating contaminated feces
  • eating soil contaminated with feces

Symptoms of whipworm infection include:

  • Blood in stool
  • However, many dogs show no signs of whipworm infection

Canine whipworm infections in people are so rare that it is not considered a threat to human health by the Companion Animal Parasite Council or the Center for Disease Control and Prevention (although we humans have our own species of whipworm which is spread between people via contaminated soil).

Over-the-Counter Dewormers

If your vet confirms that your puppy needs to be treated for worms, be sure that you know what type of worm to treat for. Over-the-counter dewormers can be less expensive than prescription, but if you’re treating for the wrong worm, your money is going to waste.

Age range: 3+ weeks

Active ingredient: Praziquantel

Target parasites: Dipylidium caninum and Taenia pisiformis tapeworms

Age range: 3+ weeks

Active ingredients: Praziquantel, Pyrantel pamoate and Febantel

Target parasites: Tapeworms (Dipylidium caninum and Taenia pisiformis), Roundworms (Toxocara canis and Toxacaris leonina) and Hookworms (Ancylostoma caninum and Uncinaria stenocephala), Whipworms (Trichuris vulpis)

Age range: 2+ weeks

Active ingredients: Pyrantel Pamoate

Target parasites: Roundworms (Toxocara canis and Toxacaris leonina) and Hookworms (Ancylostoma caninum and Uncinaria stenocephala)

Age range: 6+ weeks

Active ingredient: Fenbendazole

Target parasites: Roundworms (Toxocara canis, Toxascaris leonina), Hookworms (Ancylostoma caninum, Uncinaria stenocephala), Whipworms (Trichuris vulpis) and Tapeworms (Taenia pisiformis)

Age range: 12+ weeks

Active ingredients: Pyrantel Pamoate & Praziquantel

Target Parasites: Tapeworms (Dipylidium caninum and Taenia pisiformis), Roundworms (Toxocara canis and Toxacaris leonina) and Hookworms (Ancylostoma caninum, Ancylostoma braziliense, and Uncinaria stenocephala)

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