When to Start a Puppy on Heartworm Prevention

Published on 04/14/2025

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Preventing heartworm disease in dogs using monthly medications is more cost effective and easier than treating the condition once a dog becomes infected. Dogs of all ages should receive heartworm medication each month to protect them from this potentially fatal disease. There are a variety of year-round heartworm preventatives to choose from, including the new Credelio Quattro (lotilaner, moxidectin, praziquantel, and pyrantel chewable tablets), to ensure your dog stays healthy and protected.*

*Please see important safety information on individual product pages.

Many pet parents wonder when to start a puppy on heartworm prevention. We’ll answer this important question, plus explain why heartworm preventatives are necessary and how to choose the best one for your pet.

Do Puppies Need Heartworm Prevention?

Woman petting Beagle puppy outdoors in nature

Heartworms are transmitted through a mosquito bite. When an infected mosquito bites a dog, tiny heartworm larvae are released into the dog’s bloodstream. After around six months, these larvae mature into adult heartworms and negatively impact the dog’s heart and lungs.

Puppies are at risk for getting heartworms, just like adult dogs. Heartworm prevention is important for all dogs regardless of age. It is effective at eliminating heartworm larvae in the dog’s bloodstream before the larvae have time to mature into adults and cause significant disease.

If a puppy is tested for heartworm disease before they hit 6 months old, the heartworm test will always be negative, even if that puppy is indeed infected with heartworms. This is because those heartworm larvae have not yet matured into adults, which is the only stage that heartworm tests detect. It is essential to give puppies heartworm prevention each month to keep them protected from this dangerous disease.

When to Start a Puppy on Heartworm Prevention

Puppies should start heartworm prevention between 6 to 8 weeks of age, which is generally when the puppy first visits a veterinarian for a checkup. By starting puppies on heartworm prevention at this visit, they are protected from these parasites early on, and pet parents get into the habit of administering this preventative monthly.

Puppies under 7 months of age do not need to be tested prior to taking heartworm medication because, again, these tests only detect adult heartworms. Since heartworm larvae take around six months to mature into adults, a heartworm test will be negative if done before a puppy is at least 7 months old.

Types of Heartworm Preventatives for Puppies

When choosing a heartworm preventative for puppies, it is best to consult with a veterinarian first to learn about the pros and cons of each and find a suitable choice for your dog. Heartworm medications require a prescription from a veterinarian, they are not available over-the-counter.

Oral heartworm preventatives for puppies are the most popular among pet parents due to their ease of administration. Unlike topical preventatives, oral preventatives do not leave residue on a dog’s fur.

Some pet parents appreciate the convenience of using a combination product that protects against fleas, ticks, intestinal parasites, and heartworms. Credelio Quattro is a monthly chewable tablet that protects against heartworms, roundworms, hookworms^†, tapeworms, fleas, and ticks. It is approved for use in dogs and puppies as young as 8 weeks of age and weighing 3.3 pounds or more.¹

^†Uncinaria stenocephala

Here is a quick view of heartworm prevention products for dogs that may be recommended by a veterinarian, along with the age and weight they are suitable for:

Product	Age	Weight
Credelio Quattro	8 weeks or older	3.3 pounds or more
Simparica Trio	8 weeks or older	2.8 pounds or more
NexGard Plus	8 weeks or older	4 pounds or more
Interceptor Plus	6 weeks or older	2 pounds or more
Advantage Multi	7 weeks or older	3 pounds or more
Heartgard Plus	6 weeks or older	No weight restriction
Bravecto 1-Month Chews	8 weeks or older	4.4 pounds or more
Revolution	6 weeks or older	No weight restriction

Heartworm Prevention for Puppies: Other Tips and Advice

Since puppies grow so rapidly, pet parents generally buy medication in single doses until their dog reaches a steady weight at around 1 year of age. The strength of a puppy’s medication usually changes three to four times within their first year to account for their weight increasing.

The cost of heartworm prevention varies based on what product the puppy takes. Medications that prevent only heartworms and intestinal parasites are less expensive than medications that also protect against fleas and ticks. In general, pet parents can expect to spend between $10 and $40 each month. Once a dog reaches their adult weight and pet parents can buy larger packs of prevention containing multiple doses, it becomes more economical.

Puppies generally tolerate heartworm prevention well, but it’s always important to watch for potential side effects, such as vomiting, diarrhea, decreased appetite, or lethargy. If you notice any of these after giving heartworm medication, it’s important to contact a veterinarian.

In conclusion, year-round heartworm prevention is important for dogs of all ages to protect them against this potentially fatal disease. Speak with your veterinarian at your puppy’s first visit to discuss heartworm preventative options that would be suitable for your pet so you can ensure your pet stays happy and healthy.

Important safety information for all products listed can be found on individual storefront product description pages.

Prescription products featured require approval from your veterinarian.

All trademarks are property of their respective product owners.

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