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Is Simparica Trio Safe for Dogs?

Woman giving dog heartworm preventative
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There are numerous monthly heartworm preventatives to choose from, which can make it overwhelming for pet parents to decide which is the best option for their dog. Simparica Trio is a popular all-in-one oral preventative that protects dogs against heartworm disease, fleas, ticks, roundworms, and hookworms. 

So, is Simparica Trio safe for dogs? This medication may not be suitable for all dogs, but in consultation with your veterinarian, you can feel confident you’re using a safe and effective product for your canine companion. 

Let’s dive into what the studies show and what pet parents can expect when administering Simparia Trio for dogs. 

What Is Simparica Trio?

Simparica Trio for dogs is an FDA-approved preventative medication given once monthly to protect dogs against certain types of parasites. It is only available by prescription through your pet’s veterinarian. 

This flavored chewable tablet contains three active ingredients: sarolaner, moxidectin, and pyrantel. Sarolaner is effective against fleas and ticks, while moxidectin prevents heartworm disease. Pyrantel is a deworming medication that treats and controls two types of intestinal parasites, roundworms and hookworms

Simparica Vs. Simparica Trio

Regular Simparica is another oral chewable tablet for dogs. A benefit of both Simparica and Simparica Trio is that they both kill deer ticks (aka blacklegged ticks) and are therefore FDA-approved to prevent infections that may cause Lyme disease in dogs, a serious illness that can severely affect the joints and kidneys. 

However, regular Simparica is only effective against fleas and ticks and does not offer protection against heartworm disease or intestinal parasites. If you want to have this additional protection for your dog, Simparica Trio is a better option.

Is Simparica Trio Safe for Dogs?

SImparica Trio for dogs

When used as recommended, Simparica Trio is safe and effective for most dogs, including those who are heartworm-positive [1, 2, 3]. Dogs and puppies taking this medication should be at least 8 weeks old and weigh at least 2.8 pounds.

There are several reasons Simparica Trio may be chosen over other available products. It was the first all-in-one product to hit the market that is given once monthly to protect against fleas, ticks, heartworm disease, and certain types of intestinal parasites. (A second all-in-one product, NexGard Plus, was introduced in July 2023.) Simparia Trio was also shown to be 100 percent effective at treating heartworm disease and effectively kills five different types of ticks compared to other brands [3, 4]. 

Before prescribing this medication, veterinarians will confirm your dog meets the weight and age requirements to ensure safety. Certain health conditions, such as a history of seizures, may increase the risk of side effects, so veterinarians will carefully consider the unique health status and needs of your dog prior to prescribing Simparica Trio. Simparica Trio has not been studied in pregnant or nursing dogs, so its safety is unknown in this group. 

Because Simparica Trio contains sarolaner, which is an isoxazoline drug, it should be used cautiously in dogs who are known to have had seizures in the past or who are currently being treated for seizure disorders. It should also be used with caution in dogs who have been diagnosed with a neurological condition. Simparica Trio can cause neurological side effects, such as incoordination, muscle tremors, and seizures even in dogs without a history of these conditions, but these instances are rare. 

Additionally, Collies and Australian Shepherds can have a certain gene mutation that makes them more sensitive to ivermectin, a medication that belongs to the same drug class as moxidectin in Simparica Trio. Because of this, Collies and Australian Shepherds may experience more adverse effects from Simparica Trio than other breeds. Your veterinarian may recommend using a different monthly preventative for these breeds after an examination and discussion during their veterinary visit. 

Some dogs may experience sensitivities to one or more of the active ingredients in Simparica Trio, which can cause neurological issues or other side effects, such as vomiting or diarrhea. If adverse effects occur while your dog is taking this medication, always reach out to a veterinarian promptly. Your veterinarian may recommend you switch to another medication that is better tolerated. 

Simparica Trio for Dogs: Precautions to Consider

When administering Simparica Trio to your dog, it is important to monitor for side effects. Although this medication is usually well-tolerated in most dogs, common side effects from Simparica Trio that pet parents may see include:

  • Vomiting
  • Diarrhea
  • Decreased appetite
  • Lethargy

These side effects usually improve once the medication is discontinued. If you notice one of these side effects, it’s important to call your veterinarian for guidance. Your dog may be switched to another monthly preventative that is more suitable for them. 

Dogs need to be tested for existing heartworm infections prior to starting a preventative. Since Simparica Trio kills heartworm larvae, not adult heartworms, dogs diagnosed with heartworm disease would need to be treated with an adulticide to remove adult heartworms. In other words, if a dog is diagnosed with heartworm disease, they would need to be on both an adulticide and a monthly preventative.

There are no adverse reactions currently known for dogs taking Simparica Trio concurrently with various other medications, including vaccines, NSAIDs, steroids, antibiotics, and deworming medications. The medication can also be used safely in dogs undergoing anesthetic procedures, such as spaying, neutering, or dental procedures. Nevertheless, it is always important to have a discussion with your veterinarian about any medications or supplements your pet is taking before administering Simparica Trio. 

Pet parents should be aware that it is possible for dogs to overdose on Simparica Trio. Accidental overdose increases the risk for serious side effects, especially in breeds with sensitivities to the active ingredients in this medication. To prevent accidental overdose, pet parents should only give this medication as prescribed by their veterinarian and ensure that the medication is stored securely out of reach of pets at all times. 


  1. Mathur, S., Malpas, P.B., Mahabir, S. et al. Safety of Simparica Trio® (sarolaner, pyrantel, moxidectin) in heartworm-infected dogs. Parasites Vectors 16, 119 (2023). https://doi.org/10.1186/s13071-023-05700-9 
  2. Kryda, K., Mahabir, S.P., Inskeep, T. et al. Safety and efficacy of a novel oral chewable combination tablet containing sarolaner, moxidectin and pyrantel (Simparica Trio™) against natural flea infestations in client-owned dogs in the USA. Parasites Vectors 13, 98 (2020). https://doi.org/10.1186/s13071-020-3952-3
  3. Kryda, Kristina et al. “Efficacy of a novel orally administered combination product containing sarolaner, moxidectin and pyrantel (Simparica Trio™) against induced infestations of five common tick species infesting dogs in the USA.” Parasites & vectors vol. 13,1 77. 1 Mar. 2020, doi:10.1186/s13071-020-3945-2
  4. Kryda, K., Six, R.H., Walsh, K.F. et al. Laboratory and field studies to investigate the efficacy of a novel, orally administered combination product containing moxidectin, sarolaner and pyrantel for the prevention of heartworm disease (Dirofilaria immitis) in dogs. Parasites Vectors 12, 445 (2019). https://doi.org/10.1186/s13071-019-3702-6