In the American Heartworm Society’s 2022 survey of heartworm incidence, heartworms were diagnosed in dogs in all 50 of the United States . One in 3 veterinarians said that they felt the incidence of heartworms was increasing, while only 1 in 6 felt they’d seen better control of heartworms in their area. Heartworm medicine for dogs is the best way to protect your canine companion from these potentially dangerous parasites.
Here is everything you need to know about heartworm prevention medicine for dogs, plus a list of vet-approved picks to consider.
Why Do Dogs Need Heartworm Medicine?
Heartworm prevention medicine for dogs is essential for protecting your pet from canine heartworms, which are parasitic worms that live in your dog’s heart. These worms can be over a foot in length, and one dog can have several hundred worms. Over time, these worms cause damage to the heart, eventually obstructing flow of blood within the heart, and leading to symptoms of heart and lung disease. Untreated, heartworm disease may be fatal.
It only takes the bite of one infected mosquito for your dog to contract heartworms. Each year, heartworm disease spreads to new areas, in part due to climate change and in part due to the transport of infected dogs between states.
When a mosquito bites an infected dog, it can then spread the parasites to other dogs. Stray dogs, neglected dogs, coyotes, wolves, and foxes can all carry heartworms. The wind can blow mosquitoes for miles, so your dog may be at risk even if you’ve never seen the wildlife yourself. Keep in mind that heartworm-positive dogs in your neighborhood could also pose a risk to your pet. Rates of infections vary dramatically from year to year, so year-round prevention is best.
Types of Heartworm Medicine for Dogs
The dog heartworm medicines that we’re focused on are actually heartworm preventatives.
Treatment for dogs diagnosed with heartworm disease is not the same as your usual monthly prevention. If your dog tests positive for heartworms, your veterinarian will discuss a heartworm treatment plan with you.
Heartworm preventive medications come in a variety of forms, such as chews, tablets, topicals, or injectables. Many of these products will protect your pet from other parasites, such as fleas, ticks, or intestinal worms, but you’ll notice there are differences in what the medications cover.
All heartworm preventatives on the market belong to the macrocyclic lactone class of drugs—ivermectin, milbemycin oxime, moxidectin, or selamectin. These medications work by blocking the transmission of nerve cell signals in the parasites, effectively paralyzing and starving the worms.
Heartworm prevention requires a prescription from a veterinarian.
- Simparica Trio
- Nexgard Plus
- Interceptor Plus
- Heartgard Plus
- Sentinel Spectrum
- Advantage Multi
Best Heartworm Medicine for Dogs: 9 Vet-Approved Picks
There are quite a few heartworm medications for dogs on the market, and many of these are great options. If your veterinarian is recommending a different product from the ones we’ve included in this review, it doesn’t mean it’s not a good product. Work with your veterinarian to find the product that best suits you and your dog.
Please note that these medications are not listed in any specific order.
The active ingredients in Simparica Trio include sarolaner, moxidectin, and pyrantel. The product is a monthly pork-flavored chewable that protects against fleas, ticks, heartworms, roundworms, and hookworms. It’s not labeled for whipworms or tapeworms.
Simparica Trio is available in six dosing sizes (2.8-5.5 lbs., 5.6-11.0 lbs., 11.1-22.0 lbs., 22.1-44.0 lbs., 44.1-88.0 lbs., and 88.1-132.0 lbs.). Dogs over 132 pounds will require the appropriate combination of chewables. Dogs must be at least 2.8 pounds and at least 8 weeks old for this heartworm prevention.
The active ingredients in NexGard Plus are afoxolaner, moxidectin, and pyrantel. The product is a monthly beef-flavored chewable tablet that protects against fleas, ticks, heartworms, roundworms, and hookworms. The medication is not labeled for whipworms or tapeworms.
It’s available in five dosing sizes (4-8 lbs., 8.1-17 lbs., 17.1-33 lbs., 33.1-66 lbs., 66.1-132 lbs.). Dogs over 132 pounds will require the appropriate combination of tablets to reach their dose. Dogs must be at least 4 pounds and 8 weeks old to take this heartworm medicine.
The active ingredients in Interceptor Plus are milbemycin oxime and praziquantel. This product is a monthly chicken-flavored chew that protects against heartworms, adult hookworms, roundworms, tapeworms, and whipworms. This product is not labeled as flea and tick prevention, so a separate product would be necessary.
It’s available in four dosing sizes (2-8 lbs., 8.1-25 lbs., 25.1-50 lbs., and 50.1-100 lbs.). Dogs over 100 pounds can still take this medication but will require a combination of chewables for appropriate dosing. Dogs must be at least 2 pounds in size and 6 weeks or older to take this prevention.
The active ingredients in Heartgard Plus are ivermectin and pyrantel. The product is a monthly beef-flavored chew that protects against heartworms, roundworms, and hookworms. This medication is not labeled for flea, tick, or tapeworm infestations.
It’s available in three dosing sizes (0-25 lbs., 26-50 lbs., and 51-100 lbs.). Dogs over 100 pounds will need to take the appropriate combination of chews to reach their weight. Dogs must be at least 6 weeks of age or older to take this medication.
Tri-Heart Plus and Iverhart Plus are similar medications with the same active ingredients, which may be more cost-effective for some pet parents.
The active ingredients in Sentinel Spectrum include milbemycin oxime, lufenuron, and praziquantel. The product is a monthly beef and bacon-flavored chew that protects against heartworms, fleas, tapeworms, hookworms, roundworms, and whipworms. The medication isn’t labeled as preventing ticks.
It’s available in four dosing sizes (2-8 lbs., 8.1-25 lbs., 25.1-50 lbs., and 50.1-100 lbs.). Dogs over 100 pounds will require the appropriate combination of chews. Dogs must be at least 6 weeks old and 2 pounds to take Sentinel Spectrum.
The active ingredients in Trifexis include spinosad and milbemycin oxime. The product is a monthly beef-flavored tablet that protects against heartworms, fleas, hookworms, roundworms, and whipworms. The medication does not prevent ticks or tapeworms.
Trifexis is available in five dosing sizes (5-10 lbs., 10.1-20 lbs., 20.1-40 lbs., 40.1-60 lbs., 60.1-120 lbs.). Dogs over 120 pounds will require the appropriate combination of tablets. Dogs must be at least 8 weeks old and 5 pounds to take this drug.
The active ingredients in Advantage Multi include imidacloprid and moxidectin. The product is a monthly topical product that protects against heartworms, roundworms, hookworms, whipworms, fleas, and sarcoptic mange (scabies). To apply Advantage Multi, the fur between the shoulder blades is parted, and the liquid in the tube is squeezed directly onto the skin. The medication does not prevent ticks or tapeworms.
It’s available in five dosing sizes (3-9 lbs., 9.1-20 lbs., 20.1-55 lbs., 55.1-88 lbs., and 88.1-110 lbs.). Dogs over 110 pounds will require the appropriate combination of topical tubes to reach their weight. Dogs must be at least 7 weeks old and weigh 3 pounds to take Advantage Multi.
The active ingredient in Revolution is selamectin. The product is a monthly topical that protects against heartworms, fleas, American dog ticks, ear mites, and sarcoptic mites (scabies). This medication is applied directly to the skin in the same manner as Advantage Multi. Revolution isn’t labeled as preventing intestinal worms in dogs.
It’s available in six dosing sizes (up to 5 lbs., 5.1-10 lbs., 10.1-20 lbs., 20.1-40 lbs., 40.1-85 lbs., and 85.1-130 lbs.). Dogs over 130 pounds will require the appropriate combination of topical tubes. Puppies must be at least 6 weeks old to take Advantage Multi.
The active ingredient in ProHeart is moxidectin. This medication is injected under the skin and can only be administered by veterinary staff who have completed training and are certified to give ProHeart. ProHeart 6 is given every six months in the veterinary clinic while ProHeart 12 is given every 12 months in the veterinary clinic.
The medication prevents heartworms and treats hookworms. The medication isn’t labeled as preventing roundworms, tapeworms, whipworms, fleas, or ticks.
Dogs receiving ProHeart 6 must be at least 6 months old. Dogs receiving ProHeart 12 must be at least 12 months old.
How to Choose Heartworm Medicine for Dogs
Pet parents should work with their veterinarian to choose the best method for preventing heartworms in their pet. Things to consider include:
- How well your dog takes oral medications
- Any food allergies your dog has
- Other pets or children in the home who might touch topical products placed between the dog’s shoulder blades
- Your ability to remember to administer preventives on a regular basis
- Any reactions your pet has had to past preventives
- Your preference for having a combination product vs. administering separate heartworm and flea/tick prevention
- Your finances
In some cases, you’ll have to find the best option through trial and error. Some dogs take heartworm chews just as easily as they’d take any other treat. For these dogs, it’s a great option! Other dogs may not like the taste or get upset stomachs, so you may need to choose a different option.
If your dog experiences any side effects from heartworm prevention, make sure to notify your veterinarian. Your veterinarian can help you look at different options for your pet.
Dog Heartworm Medicine FAQ
Can you buy heartworm medicine for dogs over the counter?
Heartworm medicine for dogs can only be purchased with a prescription from a veterinarian.
Do dogs need heartworm medicine every month? Even in the winter?
The American Heartworm Society recommends that you “think 12.” Give heartworm prevention all 12 months of the year, even in the winter, and test your dog for heartworms every 12 months.
Can I give my dog heartworm medicine without testing?
Dogs over 6 weeks old and under 7 months old can receive heartworm medicine without testing. It takes around 6 months for heartworms to reach adulthood, which is necessary for the dog to test positive. Thus, a test in a puppy will always be negative. Otherwise, dogs need to have a negative heartworm test to receive prevention. It’s recommended to test dogs six months after your initial veterinary visit, again six months later, and then annually thereafter.
Does heartworm medicine make dogs sleepy?
Some dogs may act sleepy or lethargic after taking heartworm medicine.
What if I forgot to give my dog heartworm medicine?
If you are less than two weeks late, you can give the medication and continue as normal. If you’re over two weeks late, you should give your dog the next dose as soon as possible and speak with your veterinarian about retesting for heartworms in six months. If your dog goes over six weeks without prevention, they could be at risk for heartworms.
- American Heartworm Society. 2022 Heartworm Incidence Survey. Retrieved from: https://www.heartwormsociety.org/resources/vet/infographics/839-ahs-incidence-survey-infographic