dogs heartworm meds

Would it surprise you to hear vets warn dog owners about the dangers of giving their dogs heartworm meds?

The late Glen Dupree, an excellent holistic vet, was one of only a few vets who didn’t want his patients taking heartworm meds.

Dr Dupree found that a strong and vibrant immune system was enough to protect his dogs from heartworm. And he also knew that giving dogs neurotoxic drugs every month would harm that immune system.

“I assume my dogs have heartworms” said Dr Dupree. “But there’s a big difference between heartworms and heartworm disease.” And that difference is a fully functioning immune system.

There are many holistic vets who don’t recommend using heartworm meds but the pro-health approach to parasite prevention isn’t all that popular … yet.  published this article a few years back and a holistic vet even quoted it on her own page:


We hear that a lot here at DNM. But I’d like to point out that the author of this article, and most holistic vets, aren’t, well, holistic! At least in my mind.

Here’s the second part of the article, about the supposedly healthy dog Bran who shouldn’t get heartworm … but did.


Many people would think this means that a strong immune system can’t prevent worms … but I would argue (as would Dr Dupree very likely) that this was not a healthy dog with a strong immune system.

I’ll tell you why …

(NOTE: YES, you can prevent heartworm without meds! Click Here to jump to the bottom of the article and we’ll show you what simple test you can use to safely replace heartworm meds)

Heartworm Prevention: Thinking Outside The Box

I bet when you think of the immune system, you think about the protection it provides against diseases like parvo or kennel cough. What most people don’t know is the immune system also protects the body from parasites.

In fact, parasites are probably the primary indication of health! Dead animals are crawling with parasites while vibrant, healthy dogs have few or none. Most of our dogs lie somewhere in between, with probably a few heartworms or a few intestinal worms.

But again, there’s a difference between a few parasites and a large parasite load that will start to show as ill health in your dog … and that difference is the health of your dog.

The vets at the Heartworm Society agree with me:

“Single sex heartworm infections, host immune responses affecting the presence of circulating microfilariae and the administration of heartworm preventives can be factors which produce occult infections in dogs.”

An occult heartworm infection means there’s an infection of some sort but the microfilariae, or the heartworm offspring, aren’t found circulating around in the blood. So if all of the heartworms are of the same sex, or if the dog is taking preventives, then those little guys can’t reproduce and cause much of an issue.

While the vets and researchers may call this an occult infection, I might be inclined to call it a functioning immune system. Yes, that’s a novel concept for modern medicine.

Look at that quote again. If you go to the Heartworm Society, it’s easy to miss it. But there it is, nonetheless, shoved into a little corner and never mentioned again:

Host immune responses affect the presence of circulating microfilariae.

In a nutshell, this means that dogs with functional immune systems aren’t good hosts for heartworms and other parasites. The mosquito larvae (microfilaria) are killed by the immune system before they develop into adult heartworms.

That’s the good news …

The sad part is few dogs these days have a strong immune system. Do you remember Bran, that raw fed, naturally reared dog who got heartworm? This was not a naturally raised dog (nor was he healthy).

How do I know that?

He was vaccinated for rabies! Now his owner might have had her reasons to do this (and the law is a mighty good reason if you live the US), but in no way, shape or form would I call a vaccinated dog, even a minimally vaccinated dog, healthy.

Here’s why …

The Immune System And Heartworm

While vaccines can protect your dog from infectious disease, they come at a cost.

Vaccines contain mercury (yes, even thimerosal-free rabies vaccines can still contain mercury), which is neurotoxic and causes cancer. In fact, research labs will give lab animals just a tiny bit of thimerosal to give them auto-immune diseases (which include allergies, cancer, arthritis, GI diseases, etc).

Vaccines also contain aluminum, which is also neurotoxic and can cause degeneration of the brain and nervous system, especially in young dogs. And the scariest part about aluminum is that it increases the toxicity of mercury, so the “safe” levels of mercury in your dog’s vaccines are severely underestimated.

Vaccines also contain MSG as well as formaldehyde, which is one of the most hazardous and highly cancer-causing compounds known.

I don’t know about you, but I’d be very reluctant to call any dog who has been injected with these toxins, even just once, healthy. In addition, vaccines are known to suppress the immune system.

Immunologist HH Fundenberg says if your dog receives just one monovalent vaccine, his cell-mediated immunity will be cut in half … and just two vaccines will lower it by 70%.

And “all triple vaccines markedly impair cell-mediated immunity, which predisposes to recurrent viral infections, especially otitis media, as well as yeast and fungi infections.”

Sound familiar? Keep in mind, most dogs receive 3 to 7 vaccine components at a time.

Is it any wonder why dogs, even minimally vaccinated dogs, get heartworm? I hope you’re following me.

We know the immune system is responsible for protecting our dogs from heartworm and other parasites. So why would we purposely expose our dogs to things like vaccines when they destroy that immunity!

Most dogs are vaccinated with too many vaccines and much too often. It’s no wonder vets worry about heartworm.

But that brings me to …

Why I Don’t Give My Dogs Heartworm Meds

Just as vaccines can damage the immune system, so can your dog’s heartworm meds.

Now I know you’re terrified to even think about not giving your dog heartworm meds but don’t worry, I’ve got a solution for you I think you’ll like! Just keep reading.

But you need to know that all drugs carry risk and adverse reactions.

What are those risks?

I can only guess because, to my knowledge, nobody has tested heartworm meds for more than a few weeks. We have absolutely no idea just how toxic they are when given every season for the lifetime of your dog.

So the best guess we have is the adverse reactions that occur right after taking heartworm meds. Here they are:

Heartworm Medication Side Effects

HEARTGARD and TriHeartPlus (ivermectin):

Depression/lethargy, vomiting, anorexia, diarrhea, mydriasis, ataxia staggering, convulsions and hypersalivation.

INTERCEPTOR (milbemycin oxime):

Reports the above reactions plus weakness.

SENTINEL (milbemycin oxime):

Reports vomiting, depression/lethargy, pruritus, urticaria, diarrhea, anorexia, skin congestion, ataxia, convulsions, hypersalivation and weakness.

REVOLUTION® (selamectin), Topical Parasiticide For Dogs and Cats:

Pre-approval reactions of vomiting, loose stool or diarrhea with or without blood, anorexia, lethargy, salivation, tachypnea, and muscle tremors. Post-approval experience included the above plus pruritis, urticaria, erythema, ataxia, fever, and rare reports of death and seizures in dogs.

Proheart 6:

Severe allergic reactions (anaphylaxis): facial swelling, itching, difficulty breathing, collapse;  lethargy (sluggishness); not eating or losing interest in food; any change in activity level; seizures; vomiting and/or diarrhea (with and without blood); weight loss; pale gums, increased thirst or urination, weakness, bleeding, bruising; rare instances of death. This product was voluntarily withdrawn from the market in 2004 because of deaths but has been reintroduced.

Here’s the way I look at it …  these meds work by poisoning and killing microfilariae.

If they’re toxic for heartworms, they’re toxic for your dog.

And for my dogs, even a little bit of poison isn’t something I would subject them to. It weakens their immune system and makes them more susceptible to all the other diseases out there.

How To Stop Giving Your Dog Heartworm Meds

Now I know you may be reading this and thinking “I’m not going to stop vaccinating my dog and stop giving heartworm meds … you’re crazy, Dana!”

You have every right to think that way. Heartworm is a scary disease that could threaten your dog’s life. And the treatment is costly and really rough on your dog.

But what if I told you it’s possible to protect your dog from heartworm without using those meds?

Here’s some news for you … heartworm meds don’t prevent heartworm at all … they kill heartworm larvae that are already in your dog.


The only prevention they offer is killing the mosquito larvae (microfilaria) before they develop into adult worms, which migrate to your dog’s pulmonary artery and cause heartworm symptoms.

Your dog’s heartworm meds work by killing those little larvae or microfilariae. Once they develop into adult heartworms, however, it’s dangerous to use those meds to treat your dogs.

That’s why your vet wants you to give your dog heartworm meds every month. But what he likely didn’t tell you is that it takes 5 to 8 months for those microfilariae to mature into adult heartworms. Seems like a lot of unnecessary poisoning of your dog, doesn’t it?

Caution: This does not in any way mean you should give your dog his heartworm meds every 5 months.

But it does allow you to replace those dangerous meds with well-timed testing!

Replacing Heartworm Meds With Testing

So we know heartworm meds can kill microfilariae but shouldn’t be used to treat adult worms. We also know it takes at least 5 months for microfilariae to develop into adult heartworms.

So why are you giving your dog these toxic meds every month when all you have to do is just run a test at the right time?

Depending on where you live, you would only need to test once every four months, or once to three times a year. Not only can this eliminate one more toxin from getting into your dog, it will probably be cheaper than giving heartworm meds.

Your dog’s heartworm meds probably cost from $5 to $20 per month, depending on his size. You probably also test in the spring before starting the meds if you live in a colder climate. Testing is typically $30 to $50 per test.

So if you have a medium sized dog and you live in the Chicago area, you’re probably in for $150 per year if you spend $10 a month on meds and $30 for your spring test.

But what if you just tested every four months instead of buying those meds?

Your cost would be $90 (actually, it would be less as you would only need two tests in that area). Not only is it cheaper to use testing instead of drugs, it’s a much healthier option for your dog.

[BONUS: Click here to download our Free Heartworm Prevention Guide and we’ll show you the simple test you need and how often to do the test based on where you live.]

What If The Heartworm Test Is Positive?

But what happens if your dog’s test comes back positive? What then?

That’s the beauty of testing every 4 months … you know it takes at least 5 months for the microfilaria to develop into the harmful adult heartworms, so if your dog’s test is positive, you can just give him regular heartworm meds for a bit or, if you’re holistically minded like me, you can treat him holistically with the help of your holistic or homeopathic vet.

Your dog will never get adult heartworms if you do this and you can avoid the dangerous and costly heartworm treatment your vet warns you about.

[Related: There are also alternatives to treat your dog if he gets heartworms. Find them here]

One More Reason To Dump The Heartworm Meds

You might have heard that heartworms are becoming resistant to heartworm meds.

That’s absolutely true. And the more we use the drugs, the less effective they become. In the US, more and more dogs each year are getting heartworm while on heartworm meds.

Yet ironically, the American Heartworm Society responded to these reports by urging pet owners to give heartworm meds year-round. Why do they think giving heartworm meds more often is the answer?

Well, it might have something to do with the companies who fund them …


… wouldn’t you think the people who make money from heartworm meds would want you to take them more often?

Of course they would … they’re running a business.

But that doesn’t mean you have to buy their products. To me, heartworm meds have no place in my dogs’ health care.

It’s ludicrous to feed my dog a small amount of poison every month and think I’ve made him less likely to get sick. Yes, he might have less risk of heartworm, but my dog (and your dog too) statistically has a 50/50 chance of getting cancer.

That’s right … 50/50.

I think it’s my job to question every drug my vet wants him to take … and in the case of heartworm meds, the answer is a no-brainer.

So in summary, here’s why I don’t give my dogs heartworm meds:

#1 Heartworms are becoming resistant and even dogs on meds are getting them

#2 Heartworm meds contain toxic ingredients that make my dog more likely to get heartworms and other parasites

#3 Heartworm meds can easily be replaced with regular testing

#4 Testing is cheaper than giving the meds (not that cost is usually a consideration when it comes to my dogs!)

[Related: Our most comprehensive heartworm article yet. Click here]