Are Heartworm Meds Worth the Risk to Your Dog

Heartworm is one of those things most vets warn us about, usually with a prescription in hand. But here’s something most pet parents don’t know, it actually takes a perfect storm of conditions for your dog to get heartworm. And once you understand that, you’ll see why monthly meds may not be the smartest (or safest) choice. 👍

The first time my vet brought up heartworm “prevention” for Zaner was before a trip to Phoenix. Honestly, I didn’t even know what heartworm was at the time. So I asked how exactly my little guy could get heartworm in Arizona. The answer? “Mosquitoes in warm climates transmit the disease.”

Technically true… but definitely not the whole story.

And here’s the kicker: I’m from Saskatchewan, where the mosquito is basically our unofficial provincial bird. If heartworm was such a massive threat, why hadn’t anyone ever mentioned it here? Meanwhile, in all my trips down south, I’d never even seen a mosquito in Arizona. So why the sudden sales pitch?

Naturally, I had to dig deeper. And what I discovered was…

The Perfect Storm: How Heartworm Actually Happens

For heartworm to take hold, all of these steps have to line up just right:

1. A female mosquito bites an infected animal (like a dog, coyote, or fox). Only female mosquitoes transmit heartworm.

2. The mosquito incubates the baby worms (microfilariae). They need 10–14 warm days to develop into the infective larval stage (L3). This only happens if temperatures stay above about 14°C (57°F) the whole time.

3. That mosquito must then bite your dog, depositing larvae into the skin.

4. The larvae have to survive your dog’s immune system and migrate through the body for 50–70 days.

5. Finally, they must reach the heart and lungs, where they mature into adults — a process that takes about 6 months from the original bite.

That’s a lot of hurdles! Your dog’s immune system naturally clears many larvae before they can do any harm.

Why the Drugs Aren’t What You Think

❗️ Heartworm meds are marketed as “prevention,” but they don’t stop mosquitoes from infecting your dog. They only kill larvae that are a few weeks old — not adults.

⚠️ They’re neurotoxic which means toxic to the nervous system, in other words, a substance that can harm the brain, spinal cord, or nerves. If something is neurotoxic, it can mess with how your pet’s nerves send messages, which is why side effects often look like shaking, seizures, weakness, or behavior changes and we can see other side effects like vomiting, diarrhea and lethargy.

🐾 Mosquitoes are becoming resistant to these drugs, so protection isn’t guaranteed. And when 60–69% of dogs experience side effects, it’s fair to ask...is the risk really worth the so-called “protection”?

Smarter Protection: Test, Don’t Guess

Instead of relying on risky meds, talk to your vet about the 4DX test (Idexx SNAP 4DX).

• It screens for heartworm exposure and tick-borne diseases like Lyme, Ehrlichia, and Anaplasma.

• Best practice: run the test twice a year

  • Early spring (April/May) to confirm your dog didn’t pick up heartworm or tick disease over the winter.

  • Late fall (October/November) to ensure they’re clear after the mosquito and tick season.

🌿 Natural Repellent Toolkit for Dogs

If you want to skip the chemicals, here are safe and effective ways to help keep mosquitoes (and other pests) away:

🐾 Neem (topical only) – A natural oil that repels mosquitoes, fleas and ticks. Use as a diluted spray, in pet-safe shampoos, or lightly on collars before walks. (Never give neem internally and it is not for cats.)

🐾 Garlic  – Believe it or not, small amounts of food-grade garlic make dogs less appealing to biting bugs. It works from the inside out as a natural repellent.

🐾 Cedarwood & Lemon Eucalyptus Oils – These essential oils are proven mosquito deterrents. Look for pet-safe sprays or diffusers formulated specifically for dogs.

🐾 Healthy Immune System – A strong immune system makes it harder for heartworm larvae to survive if exposure happens. Fresh food, exercise and supplements like immune boosting mushrooms all play a role.

🐾 Pumpkin Seeds (bonus) – While they don’t prevent heartworm, ground organic pumpkin seeds are a natural dewormer for intestinal parasites, making them a great addition to your pup’s bowl.

📍 Check heartworm prevalence in your area, in many regions, the risk is much lower than we’ve been led to believe.

At House of Paws, our mission is to empower you with knowledge, so you can make choices that truly support your furry family’s health.