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Intestinal parasites, often called worms, are microscopic organisms that live inside your dog, where they silently cause harm. Common intestinal parasites in dogs include roundworms, tapeworms, and hookworms. Some worms, like roundworms and hookworms, can take up residence in humans, too.

If your dog has worms, you need to eradicate them quickly and prevent them from returning. Deworming medications kill the parasites your dog already has, and intestinal parasite preventives, most of which are given monthly, prevent future worm infections. Some products also kill fleas, ticks, and heartworms.

Choosing among the many safe and effective parasite preventives for dogs can be difficult. After speaking to veterinarians, we chose products based on safety, efficacy, number of parasites targeted, and products' ease of use. Read more about how we selected products at the end of this guide.

Different drugs kill different worms, so you must always visit your veterinarian for a fecal test before giving your dog a dewormer. Your veterinarian can advise you on what product might be best depending on your dog's temperament and lifestyle and the parasites that are most prevalent in your area. Many of these treatments also require a prescription from your veterinarian. Learn more about how Insider Reviews tests and researches products.

Best broad-spectrum dewormer for dogs: Drontal Plus Taste Tab, $10.99 from Chewy No other dog dewormer kills as many different types of worms as Drontal Plus.

Best tapeworm dewormer for dogs: Droncit Tablets, $5.49 from Chewy A single dose of Droncit safely and quickly kills tapeworms within 24 hours.

Best oral parasite preventive for dogs: Trifexis, $120.49 from Chewy Trifexis treats and controls three common intestinal parasites, kills adult fleas, and prevents heartworm infection with just one monthly chewable pill. 

Best topical parasite preventive for dogs: Advantage Multi for Dogs, $113.15 from Chewy With just one simple monthly application, Advantage Multi for Dogs treats, controls, and prevents more parasites than any other topical product.

Updated on 5/10/2021: We rewrote this guide and selected new products after extensive research and interviews with veterinarians. 

No other dog dewormer kills as many different types of worms as Drontal Plus.

Pros: Veterinarian recommended, kills four types of worms, safe and reliable, kills all parasites within seven days, low risk for side effects

Cons: Not for puppies younger than 3 weeks old or those weighing less than 2 pounds

Drontal Plus is a safe and effective broad-spectrum dewormer that eliminates multiple types of parasites with one dose. It kills tapeworms, hookworms, roundworms, and whipworms within seven days. Just offer the Drontal Plus Taste Tab flavored chewable tablet to your dog alone or with a small amount of food.

Drontal Plus features three powerful active ingredients: pyrantel pamoate, praziquantel, and febantel, which together cover four species of tapeworms, two species of hookworms, two species of roundworms, and whipworms.

The dewormer has a very low risk for side effects and is safe for puppies as young as 3 weeks old and weighing at least 2 pounds. It requires a prescription from your veterinarian, and a vet visit is also important because your dog may have other parasites that even a broad-spectrum dewormer can't eliminate.

When using a broad-spectrum dewormer like Drontal Plus, your dog may require one or more follow-up treatments to make sure all the worms are eliminated. If your dog has fleas, they should also be treated with a flea control product to prevent future tapeworm infections.

A single dose of Droncit safely and quickly kills tapeworms within 24 hours.

Pros: Kills four species of tapeworms, works within 24 hours, easy-to-administer tablet, long-trusted brand, affordably priced per pill

Cons: Some dogs may experience salivation, vomiting, or diarrhea after taking; not for puppies less than 4 weeks old

One Droncit tablet works to paralyze and eliminate the four most common species of tapeworms within 24 hours. Its active ingredient, praziquantel, is effective and safe for adult dogs and puppies 4 weeks of age and older. The tablet can be fed whole or crumbled and mixed with food.

The treatment is conveniently and affordably sold per pill, unlike the other tapeworm dewormer we considered, Bayer Tapeworm Dewormer, which contains the same active ingredient praziquantel but is only sold in a five-pack.

Dogs commonly become infected with tapeworms by ingesting fleas. For this reason, it's important to treat your dog for fleas to prevent future infections.

Trifexis treats and controls three common intestinal parasites, kills adult fleas, and prevents heartworm infection with just one monthly chewable pill. 

Pros: Protects against three intestinal parasites, heartworms, and adult fleas; once-monthly treatment; safe for dogs and puppies 8 weeks of age and older weighing at least 5 pounds; tablet is easy to administer

Cons: Does not kill or treat tapeworms, not labeled for use in puppies younger than 8 weeks or weighing less than 5 pounds

Our pick for best oral parasite preventive for dogs is Trifexis, a chewable tablet that treats and controls hookworms, roundworms, and whipworms. It also kills adult fleas and prevents heartworm.

Given once every 30 days, Trifexis uses spinosad and milbemycin oxime to prevent, treat, and control parasites. While it does not kill or treat tapeworms, it kills adult fleas, which are responsible for transmitting the parasite. The beef-flavored flavored chewable tablet should be given with food for maximum effectiveness.

Trifexis is safe for puppies as young as 8 weeks old and weighing at least 5 pounds. However, puppies less than 14 weeks of age might experience a higher rate of vomiting than older dogs. This parasite preventive requires a prescription from your veterinarian as well as a current negative heartworm test. It should be used with caution in dogs with a history of seizures or breeding females.

With just one simple monthly application, Advantage Multi for Dogs treats, controls, and prevents more parasites than any other topical product.

Pros: Kills and prevents six types of parasites, once-monthly treatment, easy to administer, safe for use in puppies older than 7 weeks and weighing at least 3 pounds

Cons: Does not kill ticks; not labeled for use in puppies younger than 7 weeks or breeding, pregnant, or nursing dogs

No single preventive covers every parasite that could harm your dog, but Advantage Multi comes close. Containing the active ingredients imidacloprid and moxidectin, the topical treatment prevents three common intestinal parasites: roundworms, hookworms, and whipworms. It also prevents flea infestations by killing adult fleas before they can lay eggs and prevents heartworm and mange mites.

Choosing between an oral or topical parasite product can be a tough decision. Sometimes dogs do better with one versus the other. "Some animals can't tolerate or have a food allergy to an oral product so they must use a topical," said veterinarian Melissa Smits, a partner at Fort Morgan Veterinary Clinic in Colorado. "Or their skin may be sensitive to a topical so an oral is better." If there are no tolerance issues, it usually comes down to owner preference.

Advantage Multi is easy to use: Just apply it every 30 days to your dog's skin at the base of the neck between the shoulder blades. The liquid medication is absorbed and dries within hours. Unlike with some of the other topical preventives, you do not need to wear gloves to apply Advantage Multi. If you get the product on your hands, simply wash them with soap and water. For the first 30 minutes after application, keep dogs from licking the application site, either on themselves or other treated dogs in the house. Children should not touch the application site for two hours after application.

You must obtain a prescription from your veterinarian to purchase Advantage Multi. As with all medications that prevent heartworm, your dog needs a heartworm test prior starting Advantage Multi and annually thereafter.

While researching and writing this guide, I drew from my eight years of experience as an assistant in veterinary hospitals and two decades of experience as a writer and editor in the pet and veterinary fields. I conducted research using the quick product reference guide published by the independent, nonprofit Companion Animal Parasite Council. This helpful reference, which includes all FDA- and EPA-approved parasite control products for small animals, lists each product's active ingredients, how the product is used, and which parasites it controls. 

Here are the main attributes I looked for:

Most dogs will contract intestinal parasites at some point in their lives. Some of the most common worms seen in dogs are roundworms, tapeworms, hookworms, and whipworms. In adult dogs, parasite infestations may cause mild to moderate digestive symptoms like vomiting, diarrhea, and gas. However, heavy infestations, especially in young puppies, can lead to severe issues.

"They can cause intestinal problems, malnutrition, anemia, growth problems in puppies, and even potential autoimmune issues," Smits said. "Also important is the zoonotic risk — potential spread to human family members."

Veterinarians recommend a broad-spectrum parasite preventive that treats, prevents, or controls intestinal parasites like roundworms, tapeworms, hookworms, and whipworms; heartworms; fleas; and ticks.

"Many adult dogs may be asymptomatic carriers," according to Kelley Lay, a relief veterinarian who practices in Nashville, Tennessee. "Parasites are not always able to be seen in feces and so you may not even know the problem is there. This can lead to infections that linger undetected for a long time."

Veterinarians recommend keeping dogs on a broad-spectrum parasite preventive all year, not only in the spring and summer months. Different parasites are active during different months, and parasite activity varies. Parasites can also become active earlier than expected, including during the winter.

"You cannot fully predict or control the environment your dog is in," Smits said. "I live in Colorado, which overall has a low incidence of heartworms and [has] freezes with no mosquitos in the winter. Except, I have killed mosquitos in my house in February. My dogs find rodents in the backyard with tapeworms and potentially fleas. We just found tapeworms in February."

Although different parasite preventives cover many different parasites, no one product covers every single internal and external parasite that could affect your dog. For instance, one product may cover fleas, heartworm, and intestinal parasites, but not ticks. Another may cover fleas, ticks, and intestinal parasites, but not heartworm. Talk to your veterinarian to help you decide which product will be best for your dog.

"This is the most important part of having a relationship with a veterinarian in your area," Smits said. "We are trained to know what parasite problems we have in our area are, what lifestyle risks are important to consider, and overall, what is best for an individual pet and lifestyle."

If you suspect your dog has worms, it's important to take them to the veterinarian for a physical exam and a fecal test to determine what type of worms they have.

"Not all intestinal parasites are created equal and there is not a one-size-fits-all when it comes to deworming medications," Lay said. "Your veterinarian will perform the appropriate tests to diagnose which type of intestinal parasites are present, and therefore which medication will appropriately target the problem."

Even though some dewormers do not require a prescription, do not skip the vet visit since different drugs treat different worms. Although a broad-spectrum dewormer kills several different types of worms, certain single-celled microscopic parasites (protozoa), including coccidia and Giardia, cause symptoms similar to those caused by intestinal parasites, but they are not true worms. They require different prescription medications to treat them.

In addition to conducting a fecal test, your vet can also determine if your dog may have other health issues that need to be addressed. Depending on the type of worms found, your dog might need follow-up deworming and a follow-up fecal exam to ensure no parasites remain.

Check with your veterinarian before using natural dewormers with your dog. "While 'natural' deworming products may have some effect on intestinal parasites, I've consulted with numerous clients over the years who have tried them with repeated failure," Lay said. "Also, there's unfortunately still many unknowns and variables when it comes to many of the natural products."

Lay noted that conventional, veterinarian-recommended dewormers are both effective and safe to use. "Like any medication, we can't assume there will be zero side effects 100% of the time, but the veterinary-approved products have been around a long time, have gone through stringent drug trials and studies, and are proven to carry minimal to no risk," she said.

We consulted with two licensed veterinarians for advice regarding the treatment and prevention of intestinal parasites like tapeworms, roundworms, and hookworms as well as heartworms and ectoparasites like fleas, ticks, and mites. Although this information guided us in our product selection, our experts did not specifically endorse or recommend any of the products in this guide.

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