If you’ve ever watched your dog scoot across the carpet or noticed something unusual in their stool, you may already be familiar with the unsettling world of intestinal parasites. Deworming in dogs is one of the most essential aspects of responsible pet ownership — yet it’s a topic many dog owners don’t fully understand until there’s a problem. Whether you’re caring for a new puppy or keeping an adult dog healthy, knowing how dewormers work, which worms pose a threat, and how to prevent future infections can make all the difference for your dog’s long-term wellbeing.
To break it all down, we consulted two veterinary experts: Jaclyn M. Coble, DVM, CCRP, CVA, founder of Sea Legs Integrative Veterinary Health in Boston, and Carol Osborne, DVM, founder of Chagrin Falls Veterinary Center & Pet Clinic in Ohio.
What Is Deworming in Dogs?
Deworming is the process of using medications known as anthelmintics to identify, target, and eliminate parasitic worms from a dog’s body. These aren’t harmless garden worms — they’re internal parasites that invade a dog’s intestines, organs, or bloodstream, feeding on blood, tissue fluids, and nutrients.
How Do Dog Dewormers Work?
According to Dr. Coble, dog dewormers contain active ingredients that either paralyze the worms’ nervous systems or interfere with their ability to absorb nutrients. Once paralyzed or killed, the worms are eliminated from the dog’s body through normal bowel movements.
The specific dewormer used depends on the type of parasite involved, which is why a proper diagnosis from a veterinarian is always the recommended starting point.
What Does Deworming Cost?
The cost of deworming varies based on the type of medication, your dog’s size, and the severity of the infection. Beyond the price of the medication itself, you may also need to budget for a fecal exam to identify which worm is present and a veterinary consultation. In more serious cases, your vet might also recommend blood work or imaging. Dogs with severe infestations may even require hospitalization, which adds to the overall cost.
Which Worms Commonly Affect Dogs?
Dr. Osborne identifies several types of parasitic worms that frequently affect dogs. Each has its own mode of transmission, symptoms, and treatment approach.
Roundworms
Roundworms are the most prevalent intestinal parasite in dogs, particularly in puppies. These long, pale, spaghetti-like worms live in the intestines and are transmitted through contaminated feces, soil, infected prey, or from mother to puppy via the placenta or milk.
Early infections may show no signs at all, but heavy infestations can cause a pot-bellied appearance, weight loss, dull coat, diarrhea, vomiting, and visible worms in the stool or vomit.
Hookworms
Named for the hook-like mouthparts they use to latch onto the intestinal lining, hookworms feed on tissue fluids and blood. Dogs can pick them up by eating infected prey, ingesting contaminated soil or grass, or through larvae penetrating the skin or infected mother’s milk.
Because hookworms cause internal blood loss, they’re especially dangerous for young puppies and can be fatal in severe cases. Symptoms include pale gums, bloody diarrhea, significant weight loss, skin irritation, poor coat quality, coughing, and failure to thrive in puppies.
Tapeworms
Tapeworms are segmented parasites that attach to the wall of the small intestines. The most common species in dogs, Dipylidium caninum, is typically acquired by accidentally ingesting an infected flea or consuming an infected rodent. Adult tapeworms can grow up to 11 inches long, and segments break off and appear in the dog’s feces or around the anus — often resembling grains of rice or small moving segments.
Other signs include scooting behavior, stunted growth in puppies, anemia, and in rare cases intestinal blockage.
Whipworms
Whipworms are small — roughly a quarter of an inch long — but they can cause significant inflammation in a dog’s large intestine. Their eggs are shed in feces and can remain viable in the environment for up to five years, posing an ongoing risk to other dogs.
Common symptoms include chronic diarrhea (sometimes bloody), straining during bowel movements, decreased appetite, weight loss, and anemia.
Heartworms
Heartworms are in a category of their own. Rather than targeting the intestines, these parasites travel through the bloodstream to the heart and lungs after being transmitted through the bite of an infected mosquito. The damage they cause can be severe and potentially fatal if left untreated.
Heartworm disease is most prevalent in regions with warm weather year-round, but all dogs — regardless of climate — are at risk. In the early stages, many dogs show few symptoms. As the infection progresses, signs may include a persistent mild cough, reduced tolerance for exercise, fatigue, weight loss, and a swollen belly caused by fluid buildup from heart failure.
How Do You Deworm a Dog?
The first and most important step is consulting your veterinarian before starting any deworming treatment. They can evaluate your dog’s overall health, confirm the presence of worms, identify the species, and recommend the most appropriate medication and treatment schedule.
Dewormers are available in several forms — tablets, chewable treats, liquid suspensions, powder added to food, or topical treatments. The two main types include:
- Broad-spectrum dewormers: These contain multiple active ingredients and are designed to treat a range of common parasites simultaneously, including roundworms, hookworms, whipworms, and tapeworms.
- Targeted dewormers: These contain a single active ingredient aimed at one specific parasite and are typically used when a diagnosis has been confirmed.
Dewormers can also be classified as prescription or over-the-counter (OTC). Prescription products are often more potent and are used under veterinary guidance, while OTC options may be appropriate for certain mild infections.
Always follow the dosage instructions carefully based on your dog’s weight, and repeat treatments as directed by your vet.
Side Effects of Deworming
Most dogs tolerate deworming medication without any issues. However, Dr. Osborne notes that some dogs may experience mild, temporary side effects, including:
- Lethargy
- Nausea or vomiting
- Diarrhea
- Decreased appetite
The severity of side effects generally correlates with the severity of the infection — dogs with heavier worm burdens may react more noticeably. If your dog shows any concerning symptoms after treatment, contact your veterinarian. Seek immediate veterinary care if symptoms are severe.
How Often Should You Deworm Your Dog?
The frequency of deworming depends on your dog’s age, lifestyle, and level of parasite exposure.
Puppies
Deworming typically begins at 2–3 weeks of age and continues every two weeks until puppies are weaned, according to Dr. Coble. Puppies are especially vulnerable because their immune systems are still developing, and they can acquire worms from their mother before birth or through nursing. After weaning, monthly deworming is generally recommended until the full vaccination series is complete, usually around 4–5 months of age.
Adult Dogs
Healthy adult dogs are typically only dewormed when worms are detected or strongly suspected, says Dr. Coble. However, all adult dogs should be on year-round heartworm prevention, which often includes ingredients that also help control common intestinal parasites.
Dogs with higher exposure risk — such as those that frequent dog parks, live on farms, or participate in hunting or field sports — may need more frequent fecal testing and treatment, according to Dr. Osborne. Ideally, annual or biannual stool tests are recommended for all adult dogs.
How to Prevent Worms in Dogs
Complete prevention isn’t possible, but you can significantly reduce your dog’s risk with a few consistent habits:
- Year-round flea control: Since fleas can carry tapeworm larvae, keeping fleas off your dog is a critical step in parasite prevention. Flea collars, topical treatments, and oral medications are all effective options your vet can help you choose from.
- Heartworm prevention: A monthly heartworm preventive — tested and prescribed by your vet — is one of the most important things you can do for your dog’s health. Many heartworm preventives also help control roundworms and hookworms.
- Clean environment: Regularly remove feces from your yard and living areas, wash your dog’s bedding frequently, and sanitize any spaces your dog spends time in.
- Monitor stool and behavior: Loose, bloody, or abnormal stools are worth paying attention to. Dr. Coble recommends keeping an eye on your dog’s bowel movements as a simple but effective monitoring tool.
- Regular vet checkups: Annual or biannual wellness exams allow your vet to assess your dog’s health and catch any parasitic infections early — before they become serious.
Keeping Your Dog Worm-Free
Deworming is a routine part of dog health care, not something to fear. With regular monitoring, appropriate preventive medication, and a clean living environment, most worm infections can either be prevented or treated effectively before they cause lasting harm. If you’re unsure whether your dog needs deworming or which product is right for them, your veterinarian is always the best resource.
Don’t forget: cats are also susceptible to many of the same parasites described above. Talk to your vet about parasite prevention for all the pets in your household.
Expert input provided by: Jaclyn M. Coble, DVM, CCRP, CVA, Founder of Sea Legs Integrative Veterinary Health, Boston; and Carol Osborne, DVM, Founder of Chagrin Falls Veterinary Center & Pet Clinic, Chagrin Falls, Ohio. Content medically reviewed by Chewy vets.