Not long ago, I wrote about a couple of chewable flea and tick preventatives that are somewhat new on the market that use pesticides as the active ingredients. Preventatives such as afoxolaner and fluralaner are newer forms of pesticides that work in the dog’s bloodstream to prevent flea and tick infestations, and were recently discussed on this site. I wanted to find out what studies had been run on these pesticides, and what anecdotal evidence existed about efficacy, and was surprised to learn about brief limited studies performed prior to the release of these products. I understood this lack of testing should affect how people go about choosing a flea or tick preventative.

Since writing about these preventatives, I have received a few offline messages regarding people who had lost their dogs after administering the product. Here is one of the accounts I received from Deborah Mellor, about her samoyed who passed away not long after a Nexgard treatment. Her family wanted to share her story, which can be found below (edited slightly for clarity).


My 15 year old samoyed was my pride and joy, and we did not give her chemicals at all. She had a bad flea infestation this year, and we did many things. She had a topical treatment at the vet on July 6th, later two doses of Capgard [Editor note: according to product directions/FAQ can be given with preventatives for quick killing of fleas], and then on July 30th was given Nexgard by the vet. I didn’t want to give her the pill but there were still fleas on her, so I was advised by the vets office to give her this Nexgard. Her walking was becoming difficult to begin with, and when I asked them “are you sure it is ok to give it to her”… stupid me I should have not given the Nexgard to her. The next day she could not walk, I believe it messed with her neurological system. 24 hours later she would not even get up, like she was afraid and unable to. She could not and would not get up – she was incapable of standing, as she would just fall.

She was put to sleep today [July 31st 2015]. I do not have proof but I asked the vet if it could be from Nexgard, and the vet said absolutely not. It is too late for my girl but i want to prevent this from happening to others. — Deborah Mellor

UPDATE: There are two very active groups on Facebook about these two drugs. There are regular postings added about dogs who are experiencing similar and severe side effects not long after taking these drugs, suggesting there may be a link between the two. Do remember that this is anecdotal evidence, but it can be useful to help arrive at a decision provided the limited studies and limited time the drug has had on the market.
Bravecto group
Nexgard group

Things to consider before choosing a flea or tick preventative that contains pesticides

The above story is heartbreaking. The samoyed’s family did the best they could regarding her care using the advice of a professional, but they lost her due to a reaction. While we don’t know exactly what happened (accumulation of several products, reaction between products, some other underlying condition that cropped up due to a suppressed immune system caused by the drugs, or something else), it’s a cautionary story particularly because what happened was right after the dog was administered preventatives under the direction of a professional.

And sadly, it’s difficult or impossible to ever pinpoint the exact cause of such a reaction. The studies for many preventatives (including the active ingredient of Nexgard) are short, thus not providing evidence we might need to determine a reaction was caused by the pesticide administered. The study for many of such drugs are run on a small number of young healthy dogs for a short period of time, so it’s safe to assume many variables are not studied (age, breeds, ailments, interactions, and so on). If you don’t know it can cause a problem (because they aren’t thoroughly tested for), perhaps it’s harder to lay blame when it does. Or if the problem is caused because the drug no longer lets the immune system do its job, the blame is placed on that other ailment (cancer, IMHA, etc), and perhaps not on the thing that caused that to happen (the pesticide use). Therefore, anecdotal evidence can be considered alongside many other factors to help you arrive at a final decision regarding care.

We all need to make our own best decisions about our pets for their safety and well-being, especially when dealing with something as serious as a pesticide that enters the blood stream and can affect the immune system. After caring for dogs, these are my personal considerations I make when drawing a conclusion about administering pesticides or similar products. I encourage everyone to research what they can and draw their own conclusions, and provide the following as a guideline for some of the items you may want to consider, think about, or look into further. I encourage you to leave your own considerations, experiences, and thoughts in the comments for this article as well.

My thoughts on the research phase:

  • Anything that is used in or on a dog for a long period of time should be researched with the utmost care as it will have a great impact on overall and longterm health. This can include pesticides, but is also relevant to food, lotions, and other supplements.
  • Never forget about how the product you are about to use affects the immune system. A depressed immune system leaves your dog susceptible to serious ailments, such as cancers and auto-immune disorders. It can also allow pests to flourish, such as heartworms – so a strong immune system can in some cases be used as a pest repellent on its own. Tumors affect more than half of all dogs, and more than half of all senior dogs die due to cancer. This is an incredibly high number, and my feeling is it could very well be in part due to the high exposure to pesticides (both in products such as these, and those used in our environment). If the product you are about to use suppresses the immune system, consider it something to use only when the dog absolutely requires it because he or she does not have any other options.
  • How much can you learn about the product? Or is the product not thoroughly studied (therefore presenting a risk of the unknown)?
  • If the product is new, is the product you are administering similar to anything that has been on the market for a longer period of time?
  • If called “natural”, is it actually true? Many products that are marketed as “natural” aren’t, so make sure you figure out what is synthetic or how much of the product is actually “natural” (often the active ingredient is a synthetic or unhealthy chemical). For example, some synthetic versions of pesticides described as “natural” are quite different in the way they behave. See this article for one example of this.
  • Research and consider the possibility of bio-accumulation, which is when an ingredient (such as a toxin, vitamin, synthetic chemical, etc) can build up in the body over time. Is this a factor for the product? Has it even been researched?
  • Look into possible interactions with other products you are administering: is anything known about how they interact? Has that been studied?
  • Read anecdotal stories: If the product does not have thorough research, is there anecdotal evidence of a problem? Accuracy is always a concern, but a product with a lot of anecdotal evidence of causing illness or death could/should point to a legitimate problem.

Working with vets and a prescription or recommendation:

  • Measure how much your dog is at risk: is there a lot of heartworm in your area? Is there a regular, heavy exposure to ticks?
  • Consider risk to benefit ratios: Does the problem this product solve worth the risk the product presents, or may present (due to lack of study)?
  • Determine if the diagnosis is correct without doubt: is your dog itching because of flea bites? Or could it perhaps be allergies or something else? Make sure you’re solving the actual problem at hand. (Note: I was prescribed a poisonous flea preventative for an itching dog, even when I told my vet “I’ve never seen any fleas, could it be allergies?” My vet said to apply Frontline anyway, and as a new dog owner I complied. I regret that decision wholeheartedly.)
  • Begin with the least invasive options if your dog doesn’t have a need for a quick solution. If those don’t work (and make sure you give it an honest try, search around, be creative), then move on to more risky/invasive measures if and when they’re called for.
  • Consider a holistic approach to info gathering, and make sure you have complete answers. Does your vet encourage or discourage these kinds of questions, or push you towards something without exploring the risks and benefits with you? Is your vet on the same wavelength regarding the type of care you wish to provide your dog, whatever that might be? Try to get a feeling for this, and never feel bad about trying to learn everything you can before reaching a decision. Your dog’s health is your responsibility, you are your dog’s advocate, and you have a right to feel like you have all of your questions answered before making a decision. What you give your dog is 100% your decision to make. Remember it is OK to research online if the sources are reputable, and you use the information to ask informed questions. So make sure, to your best ability, that the answers you receive are complete and unbiased. Trusting your vet and being on the same wavelength there is key. I was definitely not on the same wavelength as the vet who told me to give a flea-free itchy dog Frontline before even exploring allergies, as it sounds like the vet in the above story may have not heeded the concerns of the patient either (nor explored options for removing the few remaining fleas on a very senior dog with a less invasive chemical-free method after administering so many other drugs… such as a bath with Dawn dish soap or dichotomous earth).

I do not believe our dogs should be a science experiment. I hope to never play Russian Roulette with my dogs health, but if I do I hope to make it as safe as possible. It’s true we cannot know or control everything, but I do believe it’s best to go in knowing as much as we possibly can. Because at least then we know we tried to make the best decision we could at the time.

For what it’s worth, I have success using the following multifaceted approach:

  • Raw food or home-cooked diet.
  • Adding garlic and Brewers yeast as supplements.
  • Electromagnetic tags.
  • Essential oil spray as needed (on dog during a hike, or in household such as baseboards and bedding).

This has worked for over 4 years to keep our dogs pest-free, despite having fleas in our house and ticks in the environment when out on hikes.

Note: I am not a veterinarian, and this is not veterinarian advice. Please only use it as a starting point for your own research and conversation with a professional.

Do you have a story to share?

Anecdotal evidence helps other families with dogs make decisions about care. If you have been affected by any drug or product, please feel free to share your story. Send the story in as much detail as possible along with a photo of your dog to jen AT dogthusiast DOT com, and we will help share it to others on this blog. Please make sure to indicate whether you would like your name shared/credited, or to remain anonymous. And of course, the comments are always open for your stories as well.

About Author

Jen deHaan is graphic designer, small business owner, and dog person living in Bay Area, California. Jen enjoys learning about dog training and behavior, and has taken several courses and seminars since 2010. She also contributes articles to leading websites, such as Victoria Stilwell's Positively . It all started with a great dog called Mikey (aka "dude"), loved and lost but remembered forever. Jen also runs a freelance business focusing on graphic, web, and UI design at FoundPixel, and a small business creating hand crafted dog products at Stylish Canine.

  • deborah mellor

    holly was 15 1/2 and had been incontinent since november. her desire to walk and go out had diminished since around november 2014, however, she did not struggle to get up and once up did very well; ;trotted and all. but since the nexgard on july 29th the next day she could not get up, she was so upset by this she was like freaking out. like she didn’t know what it was. I didn’t know what it was. we went to the vet on that night and dr. said it was this, or that, nothing to definitive, you could run tests, etc. but it is just that she is ‘OLD’ ok. she said we could give her anti inflammatory meds, because “it could be her arthritis” just so rediculous. but then they’d want to run tests first to check out her liver, etc. so i left so bewildered but thinking she is just old and her legs don’t want to work anymore. but i took her home, thinking shell walk. she will walk. she did not . we had a horrible night. She couldn’t even stand to defecate. she was crying and all and i helped move her just enough that she could push her stool out. then she slept like a baby. next day same thing. exactly same situation occurred. we had a vet appt at 4:30 and it was like this was going to be it. she would have to go to sleep because she can not walk and will not walk again. so that is what happened. she was put to sleep on july 31 2 days after taking nexgard. any and all comments are welcomed.

  • Such a heartbreaking story, I couldn’t imagine how devastating that must be. I’m so glad you’re covering this because it’s extremely hard to find good resources regarding so many of the products available for our pets, it’s scary.

  • One more question this brings up; I know the EPA is supposed to test anything labeled as a pesticide but unfortunately as you mention the studies are small. When I was in college I remember reading about a couple of available pesticides that were tested and considered “safe” for humans but can be fatal to a fetus or small animals; shocked the hell out of me.

    • deborah mellor

      nexgard has not been tested by the EPA according to my research. I think because it is going into the dog rather than on the dog. Something like that.

      • Jeni Tolzmann

        Deb- I have started a Facebook group, Nexgard – Did it kill my Dog? Would you mind reposting your story to the group? I want to hear all stories regarding this drug and the devastating side effects is has had on our loved one. Perhaps as a group we can get something done. There is also a FB Group about Bravecto – Nexgard’s competition. The active drug in Bravecto is from the same family of drugs and the stories are the same. This is so unacceptable and needs awareness.

        • Thank you for posting about this! Here is a link to the facebook group for anyone interested: And here is a link to a Bravecto group:

        • 4louie

          My Husky Louie took nexguard after a tick and 3-4 weeks later his muscles deteriorated within two day to the point he could not walk…2 weeks later, we said good bye…

          We still have no answers from the vets as to what caused the aggressive muscle lost….we watched him waste away before our eyes…


          His symptoms were not consistent with snake bite nor another tick (although we still treated him just in case). He was not paralysed as such as he could move his feet away from tickles and with great effort try and lift his paw to shake hands however even this was short lived. It was as though something was eating his muscles and the more he tried the faster it targeted the moving bits.

          I want answers and don’t want anyone else going through what we did…. He was in his prime and not even 4 years of age.

          • Jeni Tolzmann

            I am so so sorry for what happened to Louie and for what your family had to go through. I am fully confident when I say this is directly due to Nexgard. This drug is a horrible toxic pesticide that is destroying our families. I have a Facebook Group – Does Nexgard Kill Dogs – please please join – we are there for support, answers and sharing of stories and information. When you are feeling able – this must be reported to Merial ( how to do so is on my Facebook Group ). Again, I am so sorry for your lose.

  • Sue Kottwitz

    I’m really glad you’re blogging about this. There are so many products on the market these days and its hard to know what the best thing to do. In fact, there are so many that I’m not sure any vet can be 100% sure of what they are recommending. We try hard to avoid chemicals in our lives, but sometimes it can’t be helped. Ozark summers and ticks mean that we do use chemicals, but instead of a monthly (topical) dose, we’ve found that all it takes is 1 dose for the whole summer season. Afraid that says a lot about the topical products (that monthly is probably overdosing.)

  • Jeni Tolzmann

    July 17, 2015 @ 2:04 a.m. the worst day of my life. We received “the call” from the Vet Hospital in Madison, Wisconsin….our most beloved 11 y.o Miniature Dachshund, Grettie, had passed away….her little body just couldn’t fight anymore. Nearly 4 months to the day….the first day we gave her that horrible Nexgard. It has been nearly a month and I still can’t get my hands around this. Our beginning story is the same as most…..perfectly healthy dog….lungs, heart, blood work, all perfect. Out vet tells us about this ” great new chewable”. We try it and vomiting begins – 4-6 times a day – leads to chronic diarrhea….for 6 weeks we are either at our vet weekly or calling about it – blood work comes out fine, cultures are negative….we hear the ” no, no, it isn’t the Nexgard” . Memorial Day Grettie has a Gran Mal seizure – and 6 weeks later she passed away. This time we discovered her protein ( albumin) was dangerously low. A week after her seizure, before our eyes, her stomach ” fell” and her back legs filled with such edema she could barely walk. My husband rushed her to the emergency hospital, an hour north, only to be told to get her, STAT, to UW- Madison’s Animal Hospital ( 3 hours away in the opposite direction ). We drove like mad men. Grettie’s little body was striped of Calcium and Protein. The words were, ” we have never seen an animal with such a low calcium before”. We felt we were in the right place. The University of Wisconsin – Madison is one of the country’s leading schools for Veterinary Science. The next 6 weeks were intense. We made weekly, sometimes bi-weekly visits to Madison. Grettie was put on an intense medical treatment plan. One of the many injections and medicines was a daily steroid shot ( hoping to reduce the inflammation in her intestines ). One July 16th, Grettie lost the use of her right front paw and “just wasn’t right”. We rushed her back to Madison. It was so so horrible. She developed, what we were told was, ” an extraordinarily rare – virtually never happens, bacteria infection….and after a 10 hour battle to try and save her, she had enough. The autopsy’s cause of death was Lymphangiectasia and Sepsis & Endotoxemia. Our hometown vet – who was so insistent 3 months ago that her problems had nothing to do with Nexgard – upon finding out that Grettie passed away, filed a claim with Nexgard immediately. Her has been dealing with a Dr Julie Cox, who doesn’t seem phased by information. Our vets in Madison are insistent that her lymphangiectasia wasn’t brought on by the Afoxolaner. Really? This drug is a protein binding drug – causes chronic diarrhea, flushing protein from tne intestines… We CAN NOT let this issue fall….We can not let our dogs have died in vain. Luckily for us, our hometown vet is on our side and doing all he can. Nexgard is not registered with the EPA – they forwarded me to the FDA. We are filing a formal complaint with them. Another group to contact is FARAD. ( as well as the Human Society. There is most defiantly something amiss with this drug…I don’t know…dosing in small dogs perhaps. Not doing anything, is not doing justice for the pain and suffering our most beloved family members have endured.

  • Jodi

    This is horrible, but to me it’s very typical of the US system. They pass something as ‘safe’ after x amount of years of testing, but the long term affects are not known and often times show up many, many years AFTER. We are on raw food, I use a natural spray on my dogs when we hike, I have my yard sprayed with a natural product for fleas and ticks also. As for heartguard, I use it sparingly. They tell me it’s safe, but I don’t believe them. I’m glad you are tackling this issue, I think so many people trust their vets (as well as their own personal Drs.) without question. Always question, always.

  • guest

    being skeptical about ingesting pesticides is good advice, and I stay away from these flea preventatives for the same reasons, but recommending “electronic” tags is also ignorant. unlike nexguard there is zero empirical evidence that these have any effectiveness, and if you did some research, you would realize they are 100% b.s.

  • Patti Winter

    11/2015: Center for Veterinary Medicine Adverse Drug Event Report, for Bravecto. 22 pages of adverse reactions including deaths:

    Also see the group Does Bravecto Kill Dogs:

  • Jan Philips

    I’ve just come across this item and wanted to let you know what happened to us.

    We have two dogs. Rocco, a German Shepherd (2 years old) and Finn a Labrador Retriever (four years old).

    Both dogs were prescribed Bravecto chewable tablets last year. Finn, who is a healthy as a horse, was absolutely fine. However Rocco, who has Inflammatory Bowel Disease, had an extremely bad reaction, vomiting, very bloody diarrhoea, collapsing etc, etc.

    Our vet contacted Merck, who assured her that Bravecto wasn’t the cause of the problems.

    Merck did say that it had been tested extensively and passed fit for use. However, when we looked in to it, it turned out that it has only every had a very small trial and only healthy dogs were used.

    That is really worrying, as they are assuring vets like mine that it’s ok to use on any dog and it clearly isn’t.

    Fortunately Rocco recovered but I won’t be giving anything like this to either of my dogs again and these days when my vet suggests any new treatment – I dive straight in to the veterinary medicine literature to check out what tests have taken place and what the side effects are. I don’t want to get caught out again. We were very lucky this time, from what I’ve read, others haven’t been.