The Dangers of Flea and Tick Medications

The Dangers of Flea and Tick Medications

By Sarah Griffiths, DCH

By far one of the most common questions I get asked about when it comes to dog and cat care is “Should I use flea and tick prevention?” It’s a big question and an important one. While these medications are effective at killing pests, they are also extremely neuro and hepatotoxic. In fact, almost 2000 dogs and cats have been reported to have died in North America since 2008 and over 4000 incident reports have been filed with Health Canada on the subject from 2009-2013. As we know, most of these incidents often go unreported and unrecognized as being connected with flea and tick medications so these statistics are most likely a fraction of the true number of adverse reaction cases. The Food and Drug Administration (USA) issued a statement in 2023 acknowledging the adverse neurological risks associated with giving isoxazoline-based flea and tick treatments to dogs and cats.

These drugs should be considered risky. They should be used with extreme caution and with supportive herbs and homeopathics if used. They should never be used on a monthly basis for “maintence!” We will talk about why monthly use is so damaging in the following paragraphs.

Deciding on whether or not to use flea and tick meds requires customization for individual animals. There is no one size fits all approach when it comes to fleas and ticks. I’ll share my personal and clinical experience with you, the science for and against these products and a full range of options so you can make a truly informed decision for your pets. Let’s explore the benefits and risks of these medications as well as the integrative ways you can keep fleas and ticks at bay.

The Pros Flea and Tick Medications

The pros to using flea tick meds are that you will most likely not have issues with either of these pests. Fleas carry the risk of transmitting tapeworm eggs to your pet as well as causing a lot of skin irritation and itching. Some pets are also allergic to flea saliva and this can be a really viscous inflammatory battle if your pet gets even one flea bite. Ticks can carry Lyme’s disease, a serious and painful disease that can affect the neurological and immune function of your pet.


Even though this all sounds scary, there are logical solutions to both fleas and ticks AND Lyme’s disease that do not involve poisoning your beloved pets with chemicals on a monthly basis. Let’s look at the entire picture.

The Problems Associated with Fleas

Flea seasons generally coincide with wet and temperate weather so you may notice that spring and fall are troublesome times when it comes to flea outbreaks. If your pet is allergic to fleas, you will likely notice right away if there are fleas in the house or around your pet. Intense itching, redness of the skin, chewing of the feet and other irritating symptoms may arise. This is known as flea allergy dermatitis and it can be extremely upsetting for both you and your animal. It is often the start of a downward spiral of medications, including flea and tick meds,  that can lead to extreme immune-mediated illness.

The flip side of this is that microbiome damage associated with flea and tick medications is real. We get into the chicken or the egg scenario when it comes to skin allergies. The more you sterilize your dog against parasites and bacteria on the skin, the more you damage the skin and internal microbiomes to the point of immunological chaos. It is a very slippery slope that can lead to a lifetime of stress and discomfort for your pet.

Luckily, there are some fundamental solutions that can help your pets internally and externally with alternatives to medications. Fleas can also carry tapeworm eggs which can cause intestinal parasite overload, something none of us want since tapeworms can also be passed to people! HOWEVER…. (I’m going to say that word a lot in this article), there are simple and non-invasive ways to avoid intestinal parasites without drugs – Keep reading!

The Problems Associated with Ticks

Ticks are a real concern in some areas of the world and it is important not to ignore their presence. Ticks, on their own, aren’t terribly dangerous in that once they have had a meal from your pet, they naturally fall off and continue about their day. The risk associated with ticks is the transmission of Lyme’s disease, a bacteria that can be transmitted via the blood. Deer ticks are the most commonly associated with Lyme’s disease. Not all ticks carry Lyme but if you live in arid environments with a lot of brush and/or a high deer population, you most likely live in a tick-dense area. With our rising temperatures and environmental mismanagement, tick populations have been on the rise for the past decade. Even with tick medications, you may be unable to completely keep ticks at bay. I will make myself very clear – ticks can STILL bite your dog even if they are on medications. They may die shortly after but they can still bite your dog and transmit disease.

Now, let’s talk about Lyme’s disease in logical terms. Lyme’s disease sounds terrifying and it can be if it is not detected early. Lyme can be hard to diagnose because the symptoms can be hard to differentiate from other diseases and, contrary to what the professionals are telling us, Lyme is actually not as common as you think – which is why its diagnosis is often missed by medical professionals in the animal and human spaces. In the worst cases of Lyme Disease, there is:

  • Low grade fever – and/or an initial high fever
  • Stiffness in the muscles and joints, especially the neck and back
  • Headache
  • Fatigue
  • Poor appetite
  • Swollen glands

If one or more of these symptoms persists in your pet, it is advised to have a Lyme test done to determine if your pet has Lyme’s disease. We will talk about testing more in the following paragraphs. 

The Science Against Flea and Tick Meds

Isoxazoline is the active ingredient in many popular flea and tick products. For a full list of which flea and tick treatments contain isoxasoline, check out the FDA’s adverse affects statement here. The mechanism of the drug is this:

Isoxasoline binds to chloride receptors in the muscles and nerve cells. While the pros of this are studied and marketed extremely well – in that it will cause death to fleas and ticks at an almost 100% success rate - it is also active in your pet’s bloodstream for up to 3 months (meaning that your pet’s blood is toxic to fleas and ticks) and is also binding to the chloride receptors of your dog or cat’s cell receptors…… This is clearly refelcted in the number of adverse neurological reactions that are being reported by pet parents.

Chloride is an important mineral that is needed for the following system functions:

-regulation of fluid entering and exiting the cells (eg. osmotic blood pressure)

-production of gastric hydrochloric acid

            -digestion of proteins

            -absorption of metallic minerals

            -activation of intrinsic factor (absorption of vitamin B12)

-promotion of muscle and nerve impulse induction
-maintence of electrical neutrality across the stomach membrane

-maintence of the pH balance of blood and tissues

-transportation of carbon dioxide out of the body via blood exchange

-protection from specific cancers, known literally as “chloride channel-associated cancers or CLC’s.” In humans dysfunctional chloride channels are associated with the following cancers (1):

  • Gastric
  • Colorectal
  • Brain
  • Liver
  • Breast
  • Nasopharyngeal
  • Prostate
  • Cervical
  • Pancreatic
  • Lung

Side effects associated with isoxasoline in a survey of over 2700 canines (2):

  • Tremors, ataxia, seizures
  • Death
  • Fatigue
  • Excessive drinking
  • Excessive bleeding or internal hemorrhage
  • Skin problems and itching
  • Anemia (low red blood cell count)
  • Behavioural changes
  • Digestive disturbance is also listed as an adverse effect including vomiting, diarrhea, flatulence and decreased appetite. While there are absolutely no studies (how convenient) on the effects of isoxazoline on the microbiome, we can be sure that with the digestive and skin-related side-effects associated with the drug that there is some level of microbiome dysbiosis going on when they are administrated - even IF you cannot outwardly see it. I believe that the risks go up for animals already suffering with microbiome-related illness, including skin allergies, irritable bowel disease and other microbiome-related illness. I have faith that in the coming years, studies will be done to prove that my theory is true. To learn more about how to protect your pet’s microbiome, check out my blog here.

Another popular drug used to fight fleas in pets is imidacloprid (aka Advantage and Seresto). This drug was recently shown to cause male reproductive issues and mitochondrial damage in rats. (3)

In light of the known effects of these drugs and the dots we can connect when we look into the importance of chloride channels in the body and the disease risks, would you still choose to use them? The robotic use of these chemicals without careful consideration of the gut, the nervous system and the microbiome brings a common saying to mind: “Don’t cut off your nose to spite your face.” Does this resonate for you too? Do the benefits really outweigh the risks?

How do I protect my pet from fleas and ticks without medications?

Let’s get to how you can avoid flea and tick meds without leaving your pet to handle parasite all  their own. Parasites are a legitimate concern in the environment but there is a way to live in harmony with these little pests. It is not about killing everything in sight. It’s about keeping your animals comfortable and unaffected. There’s quite a list of possibilities to consider so let’s dive in:

  1. If your pet lives solely indoors, there is ZERO need to medicate them for fleas and ticks. Period. Fleas and ticks come from outside and the risk of infestation or associated infections is much lower than the risk of adverse drug reactions.
  2. Consider the location you live in, the season and the climate. These factors will determine the risk level your pet faces when it comes to being affected by fleas and ticks. It’s important not to get stuck in autopilot when it comes to drug administration. Consider the dynamics of the environment as it changes so you can help your pet adapt. Wet/temperate weather will bring the need to check for fleas. Ticks love hot dry weather so arid climates and hot summers will promote them. There may be certain times of the year that medications may need to be considered but there are breaks in the cycles and if you can even reduce your usage, it will make a difference in terms of health risks.
  3. Flea combing should be your first step in determining if fleas are affecting your pet. It’s non-invasive and you can easily find them if you’re combing your pet daily.
  4. If your dog runs out in the bushes, always check them for ticks after an adventure. Use a tick-removal tool to completely and safely remove any ticks that you find on your dog.
  5. The most important defense against fleas is a healthy diet. When I say a healthy diet, I mean an unprocessed fresh food diet. Hands down, this will protect the integrity of your pet’s skin tissues and microbiome and protect them from infestations. It even changes the smell of your dog. By reducing processed carbohydrate, you reduce candida growth on the skin. Candida can cause your pet to smell “sweet” which is a real magnet for fleas. To learn more about why fresh food is so important, check out my dog and cat nutrition articles or stay tuned for my Ancestral Canine Nutrition and Ancestral Feline Nutrition E-books, including nutritional concepts, balanced recipes and a healthy fresh food rotation cheat sheet – coming Dec 1, 2023!
  6. Aromatherapy is a highly useful tool when it comes to your flea and tick arsenal. Some essential oils are so effective that they are recognized by Health Canada as having flea and tick-repellant actions. These oils include:
  • clove
  • tea tree
  • lemon
  • camphor
  • eucalyptus
  • geranium
  • pine and fir needle
  • neem

Aromatherapy sprays and shampoos are gaining popularity when it comes to flea and tick prevention. You can make your own spray at home or you can purchase one. My sister company makes eco-friendly canine sprays and shampoos for just that! You can click here to learn about my field and outback aromatherapy sprays for dogs (feline spray coming soon!). Canine sprays are often not feline-safe so be sure to check that all the ingredients are safe for your cat if you purchase a natural fleas spray. Neem and certain essential oils are not safe for cats.

  1. Herbs and fermented foods are another effective way to help your pet fight fleas and ticks. You can use them both internally and externally for great flea and tick-deterring benefits. Internal herbs that can be fed to strengthen the skin, feed the skin microbiome and deter fleas include:
  • coconut fibre
  • MCT oil
  • garlic
  • medicinal mushrooms
  • neem leaf (dogs only)
  • apple cider vinegar
  • broccoli sprouts
  • nettle leaf
  • fennel seed
  • wheatgrass
  • dill weed (dogs only)
  • holy basil (tulsi)
  • black pepper (dogs only)
  • cayenne pepper
  • sage leaf
  1. External flea and tick herbals that you can use topically and in your house include:
  • neem powder
  • yarrow powder
  • diatomaceous earth
  1. Natural lawn treatments in the form of nematodes – microscopic worms that natural live in soil and ground litter and kill flea larvae before they can become an issue. They are gaining popularity because they are non-toxic and eco-friendly.
  2. IF you do consider giving a treatment to your pet for fleas and ticks, protect them with the homeopathic remedy Nux Vomica. Nux vomica is well-known to support animals and humans who have been exposed to toxic chemicals.

Instructions: Give 1 dose of Nux Vomica 30C 3 times daily for 3-5 days following a flea and tick treatment. Watch your animal closely for any signs of adverse effects and, if they are severe, take your pet to your veterinarian.

Diagnostics to Consider in Flea and Tick-Dense Areas

  1. Routine fecal testing! The safest and most effective way to prevent internal parasite infestation is not to blindly deworm and de-flea your pets. It is, instead, by sending in a simple fecal test to your local veterinarian – called an ova and parasite test. This inexpensive lab study will reveal the presence of tapeworm, roundworm, whipworm, giardia and coccidia. If your pet has an infestation, you may even see worms in the stool. This is a topic for another day but I will plant the seed that if your pet has an infestation of any of the above, it is a major red flag as to the immune status of your pet. If your dog or cat is struggling with recurrent parasite overload, it’s time to work on imporivng your pet’s immune function. And that include NOT routinely using immune-damaging drugs.
  2. Routine Lyme disease testing. Before we dive in here, I must make it perfectly clear that Lyme disease caught early is treatable by antibiotics and can be resolved. The terrifying effects associated with Lyme come when the disease goes unrecognized and uncheck for long periods of time, allowing the bacteria to cause degenerative damage. If you live in a tick-dense environment and you find ticks on your dog, I recommend regular Lyme testing – ideally, every 6 months. This is done by a simple blood test by your veterinarian. The great thing about starting this practice early is that you always have a baseline on Lyme. If your dog shows a low or zero Lyme titer, it means that they have not contracted Lyme’s disease. If you are testing every 6 months, you can clearly see if that titer changes and if your dog has been exposed. If they have been exposed, they can be treated easily and effectively. This would be my personal preference in my own dog care regime over administering harmful chemicals on a regular basis.

I hope this article gives you the power to make the more educated decision about whether or not to use flea and tick medications in you pet care regime. The most important thing to remember is that there is no “one size fits all” method with flea and tick defense and it is up to you to consider all the options and outcomes. I hope there were a few new considerations for you to ponder and I wish you and your pets a wonderful week!


  1. Cancers: Chloride channels and transporters: Roles beyond classical cellular homeostatic pH or ion balance in cancers, 2022
  2. Veterinary Medicine and Science: Survey of canine use and safety of isooxazoline parasiticides, 2020
  3. Environmental Toxicology: Cytoytoxicity, morphological and ultrastructural effects induced by the neonicotinoid pesticide, imidacloprid, using rat Leydig cell line (LC-540), 2023






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