There is no “Natural” or “Holistic” Heartworm Prevention or Treatment Proven to be Safe and Effective

Much of complementary and alternative medicine (CAM) is offered either as an addition to conventional, science-based treatment or in situations in which conventional therapies are unavailable or ineffective. This doesn’t excuse offering treatments that haven’t been properly tested, and it doesn’t mean such therapies can’t do harm. However, such an approach at least avoids the harm that can come from delaying or rejecting effective treatment.

However, sometimes CAM providers actually believe their practices are an appropriate and effective substitute for conventional medicine, even in the case of serious disease. This attitude is truly inexcusable when, as is usually the case, there is no sound evidence to support the belief and when irrational and inaccurate denigration of conventional treatments is used to scare people away from medicine that could really help their pets. One of the most egregious examples of this kind of irresponsible medicine is the promotion of “natural” or “holistic” methods for preventing and treating heartworm disease in dogs.

Heartworm disease is a parasitic infestation transmitted from infected dogs (or other animals) to uninfected individuals by specific kinds of mosquitos. It is, of course, most common in areas that have both a reservoir of infected hosts and a population of the right kind of mosquitos. In the U.S., heartworm disease is quite common in warm, humid regions, and transmission often varies seasonally with the mosquito population. Heartworms can cause devastating, often fatal disease.

Fortunately, there are safe and effective medicines to prevent heartworm infestation. While all medications have risks as well as benefits, the risks of these preventatives are well understood and very, very small. Certainly, in areas where heartworm disease is endemic, the risk of preventatives pales in comparison to the risk of the disease. So despite the often hysterical nonsense about these “chemicals” and “insecticides,” the real facts are clear: heartworm prevention is safe and effective and far better for your pet than getting heartworm disease.

If your dog is unfortunate enough to become infected with heartworms, there are effective treatments. The risk of treatment is, however, significantly higher than the risk of prevention, though in most cases still far less than the risk of leaving the disease untreated. The American Heartworm Society (AHS) has a thorough discussion of the pros and cons of different treatment options, and working with your veterinarian you can almost certainly cure this disease and minimize the risks of treatment.

The AHS is also very clear about alternative therapies for this disease: “No “natural” or herbal therapies have been shown to be safe and effective prevention or treatment for heartworm disease.” And fortunately, many proponents of alternative therapies also recognize that no CAM therapies have been shown safe and effective for preventing or treating this disease. The most popular veterinary herbal medicine textbook states, “The authors do not recommend substituting an unproven herbal formula for effective conventional therapy.” Even as radical a proponent of alternative therapies as Dr. Karen Becker at grudgingly agrees that,treatment for heartworm infection is one area where conventional veterinary medicine offers valuable options [and] is preferable to leaving the dog untreated, or using unproven, alternative methods that may have no effect or even be harmful.”

Unfortunately, there are still plenty of unscrupulous companies, and sadly even veterinarians, willing to exaggerate the risks of conventional prevention and treatment and claim that unproven alternatives are safe and effective. Below is a long list of sites promoting unproven methods of preventing or treating heartworm disease. None of these have been demonstrated to be legitimate or reliable, and trusting your dog’s life to any of them is a dangerous mistake.


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86 Responses to There is no “Natural” or “Holistic” Heartworm Prevention or Treatment Proven to be Safe and Effective

  1. skeptvet says:

    The risk of heartworm disease depends on how common the parasite and the mosquitos that spread it are in your area, which is a function of climate. In some areas, no prevention is needed. In others, the risk of getting heartworms is very high without constant monthly prevention. You can get a rough idea about how common heartworm disease is in your area here. The American Heartworm Society used to recommend seasonal use of preventatives based on the length of time each year the mosquitos that spread heartworm disease were active. Unfortunately, most people simply can’t remember to start on stop preventatives on a schedule, so dogs were getting heartworm disease when it could have bene prevented. As a result, it is safer for most people to give year-round protection if you live in an area where heartworm disease exists.

    Use of a preventative 4 times a year might or might not protect your dog, but it’s a bit like playing roulette. If the preventatives are given at exactly the right time after exposure, they will work as they always do. But if they are given too early or too late, they won’t work. And since you can’t know when your dog has been exposed, this is a pretty risky strategy. Despite the problems you had with your previous dogs, tens of thousands of dogs take these products routinely without any health problems, so they are very safe. If heartworm disease is a risk in your area, I would not expect the approach you have been recommended to be safe and effective.

  2. carole says:

    my Pomeranian gets this jumping twitching leg kicking action for about 18 days after he has had his heart worm pill is this harmful? My neighbor says it is and he is putting his big beautiful dog on natural hworm pills.

  3. skeptvet says:

    I would have your vet investigate what is happening. And I would bring her a video of the behavior. My guess for a Pomeranian would be a luxating patella, which would have nothing to do with the heartworm medication, but of course no one can properly diagnose over the internet.

    The thing your neighbor doesn’t understand is that there is no “natural” heartworm preventative, so if they are not using a product that has been properly tested scientifically, they are not protecting their pet from the parasite.

  4. Greta says:

    I hope all those links you posted about unscrupulous companies and vets are no-follow links, these crooks deserve no traffic!

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  6. D. Barrett says:

    I agree that most natural/holistic remedies are snake oil.

    But… what do you think of testing the dog every 4 months for heart worms, and administering the medicine only after a positive (which presumably would be early enough that the dog could take the standard medication to eradicate the early-stage worms)?

  7. skeptvet says:

    Heartworm prevention has to be tailored to the local risk. In my locale, incidence is close to zero, so prevention is optional. In other places I’ve lived, risk is high year-round and I recommend year-round prophylaxis. The testing strategy you suggest wouldn’t work because the test identifies adult female worms, so it is not positive until there is already a patent infection. The preventative kills larval stage heartworms, so at that point it would be useless, and the adulticide treatment is much riskier than prevention.

  8. D. Barrett says:

    Thanks for the reply. We’re still on the fence, the argument being that while yes, the dog would have to go on “adulticide” treatment, the frequent testing would insure it would be a safe and more moderate regimen. Not risky (at least nothing like the risk of a dog with a long infestation (or one of unknown duration.) My understanding is, if caught that early, the adulticide treatment isn’t that much different than the normal preventative regimen. Therefore possibly worth considering. Or is that incorrect?

  9. art malernee dvm says:

    if caught that early, the adulticide treatment isn’t that much different than the normal preventative regimen.>>>>

    In my opinion the adulticide arsenic treatments needs pulled off the market. If drug makers want to continue to sell Arsenic wormers the FDA needs to make them show the patient is better off taking Arsenic rather than letting the worms die on their own.

  10. skeptvet says:

    The risk of serious adverse events or death is certainly lower when treating patients with low worm burdens. However, there is still some risk due to pieces of dying worms breaking off and blocking important blood vessels, allergic reactions to decomposing worms in the cardiovascular system or the drug itself, and pain or local inflammatory reactions to the drug. Almost none of these risks occur with the tiny doses of preventatives needed to kill larvae. There is really no advantage to the dog to letting them get adult heartworms in their pulmonary artery and then killing them there compared with giving a preventative that kills early stage larvae in the peripheral circulation. It’s not safer, more effective or less costly, so i just can’t see any reason to use that strategy.

  11. skeptvet says:

    Sorry, Art, but again I can’t take seriously the suggestion that leaving heartworm disease untreated could possibly be safer than treating it. Saying “Arsenic” over and over again is like saying “Toxin” or “Chemical”– It sounds scary but it really doesn’t have anything to do with the risks and benefits of treatment compared to no treatment.

  12. art malernee dvm says:

    If you have a real bad case of heartworms the arsenic wormers are so risky the FDA will not let you use them. (class 4). The arsenic wormers are not approved to be used in heartworm positive cats at all. By not taking me seriously are you making the claim that treating heartworms in cats with arsenic is safer then not treating with arsenic? I keep saying arsenic over and over because there is a reason all the arsenic wormers used for other worms in humans and animals have been pulled off the market. All you would need to do is treat half of the heartworm positive dogs with arsenic wormers and the other half just with macrolids fda approved to be used in heartworm positive dog and follow them out for a few years. The truth is without a good study we really do not know if the dogs are better off getting the arsenic. I am amazed that I’m not taken seriously. At least by vets who have used these arsenic drugs a lot and treated other dogs with just macrolids fda appoved for hw positive dogs when the owner refused the arsenic drugs due to cost. The FDA has determined the dogs at great risk of dying from heartworms and cats are better of not getting the arsenic wormer. I think its reasonable the fda make the arsenic wormer drug makers show dogs of class 123 are better off getting arsenic wormers before they are allowed to continue selling it.

  13. D. Barrett says:

    Thanks once again for the reply! I think I’m leaning to putting our dog on the pills, though it’s not a trivial decision. I’m not a tin-foil hat wearing anti-vaxxer that thinks fluoride in water causes herpes–but putting poison–even in “small” quantities–in a dog’s circulatory system, 24/7, is full of unknowns down the road in my opinion. After all, there’s been lots of human meds taken off the market when years later hard-to-isolate effects have emerged, and you don’t have to be an anti-science nutcase to suspect that the increased rate of canine cancer reports is at least partially due to the soup of non-naturally occurring chemicals we expose them to. I just don’t have 100% trust that the long term statistical dangers are (or ever really can be) evaluated to declare there’s an insignificant risk of cancer and other chronic issues down the line.

    Which means, if…

    1.) one is willing to religiously do frequent (every 4 month) testing, and
    2.) given the incidence of dog heartworms is (from my understanding) in the 1.5% range (and much of that may be from low resistance dog-shelter dogs so for my healthy dog it may be even lower)

    …then the risk equation looks something like:

    Less than 2% risk of dog having to undergo (relatively safe) EARLY stage Heartworm treatment


    Non-0% risk of long term exposure to a toxin in the dog’s circulatory system for its entire life

    The solution to the above really comes down to how confident you are that the methods of testing this stuff on dogs is 100% dependable, both for the long and short term. Cancers, for example, are often very hard to assign a particular cause to, but exposure to toxins is certainly a factor in many cases. Administering a toxin in your dog’s system for year after year after year just seems, intuitively, possibly worth taking the above < 2% risk of having to undergo the albeit serious but much more mitigated treatment–at worst–if you "lose".

    Of course, if I was NOT going to administer the frequent testing, there'd be no decision. I would go with the monthly (or every 6 weeks) treatment as then the magnitude of "losing" is too great in that case. Just not so sure it's such a slam-dunk when the frequent testing is factored in.

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  15. Abby says:

    We live in Central KY and will be traveling to Eastern TN soon. We have a 5 lb maltese we will be taking with us. He is generally very sensitive to vaccines and other medications, and takes approximately 24-48 hours to recover. In making the decision to pursue HW prevention, I looked at the map to see the incidence rates in these areas. Both are fairly low. Warm weather generally lasts only from May-October here. I’m assuming that’s when mosquitoes are active (correct me if I’m wrong), and if the preventative lasts for 4 months, then he would only need two per year, correct? Also, this may be a matter of personal preference, but I’m wondering how low of an incidence rate is low enough to not recommend heartworm prevention? How confident would you be in not pursuing prevention if numbers were between 6 and 26 reports per clinic? Thanks for your time.

  16. skeptvet says:

    Heartworm risk can be tricky to predict. Year-round prevention is recommended by the American Heartworm Society and the FDA because seasonal transmission can be inconsistent from year to year and difficult to predict and because people are likely to forget to resume prevention on time and so leave their pets vulnerable when transmission resumes. The best estimates for seasonal transmission for KY come from a 1998 research paper, and this suggested use of preventatives from June through December. However, local heat islands and other microclimate factors, and the general warming of the climate, all make predicting heartworm transmission difficult. Prevention only lasts 30 days (except for the 6-month injectable product), and the preventatives work by killing the larvae in the blood after exposure, so they must be given past the last date at which exposure occurred. A seasonal approach may be effective, but it is not straightforward or totally reliable.

    The other side of the issue is how much risk is there to giving heartworm preventatives, and all the evidence suggests the risk is extremely low. They are dosed by weight, so the risk shouldn’t be any higher for a small dog.

    I would consult some veterinarians in the area about their experiences with heartworm disease in their particular area since this will likely be more reliable than generic estimates such as the AHS incidence maps.

  17. From research, preventatives are shown to be effective for a previous infection dating up to 30-45 days. This has to do with the life cycle of the larvae, etc. So depending on where you live it is really not necessary to dose as often as recommended, and the reasoning is because of potential human error in itself. There are still lots of questions with using these products.
    1. Who benefits from “research” done – a natural and cheap/safe remedy – or one who research is sponsored by drug companies and pushed on consumers. Obviously those with the most research and marketing funding are the ones where there is profit to be gained – so to claim that our trust should be based in research by the same companies/ organizations profiting from the products is not exactly a sound argument 2. The constant overdosing of products which may in turn cause their natural defenses to be ineffective. There are studies about how sick or otherwise stressed animals may be vunerable to heartworm, but health animals have natural defenses.
    3. Overdosing causing resistance of the worms to those products. This is going to become a larger issue as we continue to encourage or scare dog owners in to longer than necessary treatments.
    4. Side effects and otherwise health complications from use of these products, along with other treatments a vaccinations. I can say, even with doctors that treat humans, the treatment methods are not necessarily about the patients best interest. Ive had many doctors tell me outright that the consideration of nutrition in treatments is not their responsibility and in medical school only one nutrition course is required. Just because one has a degree, license, certification does not imply that person knows everything. Talking with numerous medical students, nurses and doctors, it is up to the individual to enlighten themselves on the changing technologies and remedies and those with more money have will usually have better access to the attention of medical professionals. At least in the US, we also tend to demand short and easy solutions, rather than hard lifestyle changes.

  18. Animalover says:

    I have questions and a snippet of just some simple logic.
    1. In this day and age of genetic engineering, and it is more advanced than most may think, why hasn’t the heart worm been genetically eliminated? You know like they were doing in Fl not too long ago with mosquitos. I can partially answer my own question, there would be no need for the medications then.
    2 Unrelated if you weighed 200 lbs would you want an inoculation the size of a 3 inch cube? That is what all these supposed smart vets do with some small animals.
    Logic in the medical professions are either lacking or something else is going on.
    1 cc for a 4 lb critter = how much for a 200 lb person?

  19. skeptvet says:

    This has to do with the life cycle of the larvae

    Of course it does. The preventatives work by killing a specific larval stage, and whether or not this will be present in dogs depends on the temperature and activity of the vector (mosquitoes). If later stage larvae or adults are present, then the preventatives don’t work.

    Obviously those with the most research and marketing funding are the ones where there is profit to be gained – so to claim that our trust should be based in research by the same companies/ organizations profiting from the products is not exactly a sound argument

    The problem here is that you think you can assume a preventative or treatment is effective without research. Sure, research takes money, and much of that comes from industry because, unlike in human medicine, the government and non-profits are less likely to fund studies. However, claims that something is safe and effective still need to be backed by research or they are just guesses, and often wrong guesses.

    Secondly, there are many companies profiting from selling alternative remedies, and they have the same responsibility to prove their claims as any drug company. They often don’t, because the government doesn’t make them do so, but the argument that they can’t afford to is not legitimate when the herbal remedy and supplement market is a multi-billion dollar industry.

    The constant overdosing of products which may in turn cause their natural defenses to be ineffective. There are studies about how sick or otherwise stressed animals may be vunerable to heartworm, but health animals have natural defenses.

    I would love to see those studies because I believe this claim is nonsense (and I think it interesting that you cite studies when they support your argument but claim we don’t need them if there are none to support it). Sure, healthier animals are always more resistant to disease than sick animals. However, healthy animals are still vulnerable to many diseases, including heartworm disease, and there is no evidence that preventatives reduce any natural resistance.

    Overdosing causing resistance of the worms to those products.

    No, this is not how drug resistance works. Any exposure to a population will affect some individuals more than others due to natural variation. Over time, those individuals with some resistance to a drug will come to be a larger proportion of the population because they out-reproduce those more heavily affected by it. The major risk factor for this is actually TOO LITTLE USE of the drug. An incomplete course of antibiotics, for example, leaves more bacteria alive to reproduce and generate a resistant population than a complete course. Consistent use of a preventative is more likely to keep the heartworm population small than intermittent use. Finally, the American Heartworm Society has looked at the real evidence and concludes drug resistance is rare and not a significant cause of preventative failure in dogs. The more likely problem is inappropriate and inconsistent use, which is what you seem to be advocating.

    Side effects and otherwise health complications from use of these products, along with other treatments a vaccinations.

    These are rare, rarely serious, and far outweighed by the benefits in preventing death and disease.

    I can say, even with doctors that treat humans, the treatment methods are not necessarily about the patients best interest.

    An awful and untruthful thing to say. The arrogance to believe that anyone who disagrees with you must either be ignorant or a bad person is astounding!

    Ive had many doctors tell me outright that the consideration of nutrition in treatments is not their responsibility and in medical school only one nutrition course is required.

    Yes, I’ve heard this one before. The idea that vets know little or nothing about nutrition always seems to come from vets on lay people who have declared themselves experts after reading some popular books or a lot of web sites. “Enlightening” yourself usually means fishing around the internet for claims and ideas you like better than the mainstream scientific answer and then choosing to believe you know something the entire medical profession has missed. This is not an education in nutrition or a legitimate source of expertise. Get a graduate degree in animal nutrition or a board-certification in veterinary clinical nutrition and, while you still won’t always be right, you’ll have a lot better claim to knowing more than most vets about the subject.

  20. skeptvet says:

    1. So the implications that we have an effective method of eliminating heartworms but choose not to do it because of the money to be made on medications is an ignorant and offensive bit of conspiracy mongering.

    2. Your questions doesn’t make a lot of sense since humans aren’t susceptible to canine heartworm disease. It sounds like you may be asking about the relationship between dose of heartworm preventatives and body weight. Dose is determined not only by size but by the relative safety of a drug for the individual taking it. The reason we can safely take ibuprofen and our cats can’t is not just because we’re bigger but because we have different tolerances based on our physiology.
    So heartworm medications are very toxic to worms, and very safe for mammals because worms and mammals are very different. The doses used for heartworm prevention are incredibly tiny, and the difference between the dose a 5# dog gets and a 25# dog gets is meaningless. That is why the “cubes” are dosed in broad ranges (usually changing every 25-50#). In fact, for other kinds of parasites, we routinely use the monthly heartworm dose on a DAILY basis for dogs with no ill effects because the drugs are so safe for mammals and the monthly dose is so minuscule.

  21. art malernee dvm says:

    From the American Heartworm Society April 2001 Symposium: McCall, Further

    Evidence of Clinical Prophylactic and Adulticide Activity of Monthly Administration of Ivermectin and Pyrantel Pamoate in Dogs Experimentallly Infected with Heartworms. When started at 5 months post infection, after 36 months, HGplus was 98.7% effective in eliminating adult heartworms. Much research needs to be done to evaluate the pros and cons of this treatment vs Immiticide.The American Heartworm Society recommends radiographic evaluation before deciding on a course of treatment.

  22. greg says:

    I believe the reference to the “slow kill” method has been debunked. I believe that many of those animals that tested negative after slow kill, in fact still had circulating antigen once the samples were heated and the antigen/antibody bond was severed.

  23. art malernee dvm says:

    I believe the reference to the “slow kill” method has been debunked. >>>
    debunked by who? studies that included adding tetracyclines?

  24. art malernee dvm says:

    Greg, is this the study? 1. Ames M, VanVranken P, Plath C, Atkins C. Use of Moxidectin/Imidacloprid and Doxycycline for Non-Arsenical Heartworm Adulticidal Therapy. Proceedings ACVIM 2017.

  25. greg says:


    I am honestly not sure. The one I am thinking about has Susan Little from Oklahoma State as one of the authors.

  26. greg says:

    Basically went back on some of these dogs that were concluded to have seroconverted based on the antigen tests and then heated the samples, only to find a good percentage of these dogs actually still had circulating heartworm antigen.

  27. art malernee dvm says:

    In 2017, Marisa Ames and colleagues presented results of a study examining the use of moxidectin and doxycycline as an adulticide (Ames 2017). They gave doxycycline for 15 days, and moxidectin/imidacloprid (Advantage Multi) every 2 weeks for the first 3 months, then monthly after that. Most dogs were antigen-negative after 1 year.

  28. greg says:

    Art, I have read that as well. I believe Dr. Little’s research takes those dogs that were heartworm negative and finds that once those samples were heated, thereby breaking the antigen antibody bonds, they were, in fact, still antigen positive. it is out there, but I don’t have the time to track it down and link it.

  29. art malernee dvm says:

    The argument proposed by AHS and CAPC against slow-kill (aka trickle-kill) protocols is that microfilariae produced by the adults in these dogs are exposed to the same sorts of selection pressures as described in the experiment above – that it leads to a selection of microfilariae with a resistant genotype. These microfilariae can then mature in mosquitoes to L3 larvae that are able to withstand preventative macrocyclic lactone administration, leading to adult patent infections in the face of preventative administration (“loss of efficacy”). With sufficient spread of these resistant genotypes through the population, widespread loss-of-efficacy issues arise.

  30. Eileen says:

    Check natural pine oil.
    Turpentine oil, from pines…
    Wirks wonders for many ailments.
    For pets and humans.

  31. skeptvet says:

    No randomization, no blinding, no control group, no measure of adulticide efficacy, only 50% decrease. seen in larval stage, and absolutely no evidence that this product is of any value in treating heart worm disease. This is the research equivalent of “fake news.”

  32. RNLM says:

    Just curious. In what way is it thought that some of these natural remedies may cause harm? Here is why I ask. With a legitimate rescue I have a dog that came from a shelter in an area that has high occurrences of heartworm disease. He has gone to multiple vets, they think he is under 3 years old. He has at this young of an age tested positive for severe heartworm disease. He in CHF and has had to have enormous amounts of fluid removed from his abdomen and was severely emaciated. He is not able to currently go through conventional heartworm treatment. He has gained weight and has no symptoms of disease (CHF or HW) but must still be assessed a cardiologist at which point we hope he can go through conventional treatment more then anything. He has been on doxicylin and prednisone. As long winded as this is, I would hope that while we verify funds and make the needed appointments, it could be at least somewhat beneficial or a ‘cant hurt to try’ additional use of a ‘natural’ plant based supplement until he can hopefully have treatment…

  33. skeptvet says:

    Until something is tested properly, the “can’t hurt” claim is just as unproven as the “works” claim. People seem to think that because something is called “natural” or comes from a plant that it must be safe, but many natural plant compounds are toxic, and many people have been killed and injured by herbal remedies, so untested herbal treatments do have potential risks.

    And in the case of heart worm disease, the biggest risk is that when thee worms die they break up into pieces which get stuck in blood vessels, causing a type of stroke. Any remedy that was effective at killing heartworms would have this risk, whether it is herbal or conventional, so there is just no way a product can be both completely safe and effective in this situation, regardless of where it comes from.

    Doxycycline is a conventional treatments for heartworm disease, so even though there is more risk from a direct adulticide in a dog with heart disease, this may help reduce his worm burden and give him a chance to recover enough for fully effective treatment. Rolling the dice on untested remedies is likely to nothing at best and injure or kill your dog at worst, so I don’t recommend it.

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