Things to Consider with Flea/Tick/Heartworm Prevention and Natural Alternatives

Disclaimer: This is not veterinary advice, and for informational purposes only. I include questions to ask your vet at the bottom.

If you've sat in a vet's office and walked out with a monthly chewable for your dog without really knowing what was in it, I can relate. We trust our vets, we want to do right by our dogs, and it's easy to just say yes when the vet hands you something and says it'll protect your pet.

But here's the thing. I learned the hard way with Paisley that "it'll help" doesn't always mean "it's safe." And I don't want other dog parents to go through what I went through. So let's talk about isoxazolines, because I don't think most people really know what they are. Note: I have not had this experience with my dogs (I have not given any flea/tick preventative in years), but Paisley's ordeal was because I blindly trusted my vet about a medication that isn't safe. Now I know better, so I try and do better by educating.

So What Are Isoxazolines?

Isoxazolines are the active ingredient in some of the most popular flea and tick products like Bravecto, NexGard, Simparica, Simparica Trio, and Credelio.. These are systemic medications, meaning your dog swallows them, they enter the bloodstream, and when a flea or tick bites your dog and feeds, they ingest the chemical and die. Recently, a yearly injection was FDA approved so the isoxazoline is in your dog for a whole year, and there is not way to reverse it if your dog has a bad reaction. There are also flea collars, like Seresto (this does not contain isoxazolines, but has imidacloprid and flumethrin) on the market that fall under the same category, but potentially more toxic (see below).

They Don't Actually Prevent the Bite

These products are marketed as 'protection', but they don't stop insects from landing on or biting your dog. The insect has to bite first. It has to feed. Then it ingests the toxin and dies. That's how it works. Why does that matter? Because some tick-borne diseases can start transmitting in a matter of hours. They're really more of a systemic killer that works after the fact. That's a very different thing.

They're Neurotoxins

I want to be clear about this: isoxazolines work by disrupting the nervous system. They interfere with something called GABA-gated chloride channels, which regulate nerve activity. In insects, this causes uncontrolled neurological stimulation and death. The argument is that dogs and cats have different receptor structures, so they're less affected. Less affected is not the same as unaffected.

In 2018, the FDA warned about isoxazoline products specifically because of the risk of neurological adverse events. And in 2023, they required more strict labeling. Reported side effects in dogs include seizures, tremors, muscle weakness, vomiting, diahrea, loss of coordination, and death. These reactions are considered rare, but they are real and they are documented. And if it happened to your dog, "rare" wouldn't feel like much comfort. When another vet later told me that Paisley's death was 'one in a million', I thought I was going to punch her because my dog's death was the 'one millionth'. So insensitive.

We Don't Know the Long-Term Effects

Most safety studies are done over a short window of time. But many dogs are given these products every single month for their entire lives. What does chronic, long-term exposure to a neurotoxin do to a dog's nervous system over time? The truth is, we don't fully know yet. Some vets and dog owners have raised concerns about long-term neurological symptoms and immune issues in dogs on these protocols, but large studies are still limited.

Has your dog (or cat) had mystery health issues like seizures, ataxia, vomiting, diahrea, etc and no one can figure out why?

 I didn't fully know the long-term effects of Apoquel either, until I did.

What About You and Your Kids?

This part almost never comes up at the vet's office, and it really should. After your dog takes one of these products, residual chemicals can remain on their coat. Adults and kids who pet the dog and then touch their mouths are getting some exposure to that chemical. Children's nervous systems are still developing and are more vulnerable to neurotoxic substances than adults. Those of us with autoimmune disease definitely need to take this into consideration. The research on human exposure is limited, but if a chemical disrupts the nervous system of insects and can cause seizures in dogs, I think it's worth thinking about who else is in regular contact with your dog.

So What Are the Alternatives?

There are options! They take more effort, but they exist.

•         Natural repellents using cedar, lavender, or neem can help deter insects. Products like Wondercide and Kin + Kind make some great options- I use both. They need to be reapplied more often, but they work without putting neurotoxins into your dog's system. For the topical, I only use 2-3 drops for Birdie once a week- on her shoulders, back, and at the base of her tail. It's strong!

•         Kelp and garlic powder added to meals can actually help repel fleas and ticks from the inside out. This is important because you want to repel, not just kill after the bite. I use Flea Free Flea.

•         Tick checks and regular grooming after being outside are still one of the most effective tools available, and they cost nothing.

•         Yard management matters more than people realize. Keeping grass trimmed and clearing leaf litter reduces tick habitat significantly. I use Wondercide Lawn Spray.

• Testing more often: Instead of once a year, you can do a 4DEXX test monthly, or every 3 months.

•         Know your risk level. Hiking in the Minnesota woods faces very different risks than a dog in an urban environment with limited wildlife exposure. Make decisions based on your actual situation.

Heartworm is a more complicated conversation, because it is a serious disease and the risk of not addressing it in mosquito-heavy areas is real. There are integrative veterinarians who advocate for a more targeted approach, including more frequent testing and lower-dose protocols. Dr. Karen Becker and Dr. Judy Morgan (both veterinarians) are great resources if you want to point your vet in that direction. You can download Dr. Morgan's eBook on natural parasite prevention here. Also, here is a parasite prevalence map.

Questions to Ask Your Vet

You don't have to just nod and take what's handed to you. Here are some things worth asking:

• What is the actual heartworm and tick disease risk in our specific area?

• Are there alternatives for my dog's situation?

• What should I watch for if my dog has a neurological reaction?

• Do you have experience with a more integrative approach to parasite prevention?

• Is my dog's current diet contributing to inflammation or immune suppression that could make them more susceptible to parasites?

• What are the actual transmission times for the tick-borne diseases most common in our area, and does that change how we think about prevention?

• If my dog has a neurological reaction to a parasite preventative, what does that look like and how quickly do I need to act?

• Are there certain breeds or dogs with specific health conditions that should avoid isoxazoline products altogether?

• How often should we be doing fecal tests to check for intestinal parasites instead of just assuming prevention is working?

• If I want to take a more natural or integrative approach, are you open to working with me on that, or can you refer me to someone who is?

• Are there lower-risk alternatives for a dog that spends most of their time indoors or in a low-risk environment?

A good vet will welcome these questions.

Diet Matters More Than You Think

Here's something most pet parents don't think of in the parasite prevention conversation: What your dog eats every single day plays a huge role in how 'attractive' they are to parasites in the first place.

Ultra-Processed Food

Ultra-processed dry foods (what we call 'kibble') are made up of at least 40 percent starch. That starch converts to sugar during digestion, and sugar feeds harmful organisms in the gut, promotes inflammation, and chips away at your dog's immune system over time. And here's the part that blows my mind: intestinal parasites thrive on the starch and sugars found in kibble. A high-carb, heavily processed diet is essentially inviting the parasites we're trying to prevent.

Your dog's gut is also home to roughly 70 to 80 percent of their immune system (it is for humans, too!). When that gut is compromised by a poor diet, the whole system suffers, and a weakened immune system is exactly what parasites look for in a host.

Fleas and ticks go where they have the easiest access to nutrients, and they have their best luck with weak and unhealthy hosts. A dog with a thriving immune system, healthy skin, and a resilient gut is simply less appealing to pests than one that's chronically inflamed and nutrient-depleted.

If your dog or cat eats a whole food diet, minimally-processed food it will support a more diverse and resilient microbiome, better skin and coat health, and overall vitality. All of that makes your dog less appealing to parasites.

Preventative Whole Foods

Beyond switching to fresh food, there are specific things worth adding to your dog's bowl that can make a real difference:

•         Fresh garlic in small, size-appropriate amounts has well-documented anti-parasite and immune-supporting properties and is one of the most talked-about natural repellents in the integrative world.

•         Brewer's yeast is rich in B vitamins and creates a skin environment that fleas and ticks find less appealing.

•         Apple cider vinegar added to water can help alter your dog's skin pH, making them less attractive to pests.

•         Sardines or fish oil provide omega-3 fatty acids that nourish skin and coat from the inside out, making it harder for parasites to latch on.

•         Kelp supports thyroid and immune function and is a staple in many natural parasite prevention protocols.

You don't have to change everything all at once, so try not to focus on that. Even adding some fresh whole foods to your dog's existing meals is a step in the right direction. The goal is less processed, less starchy, and more nutrient-dense over time. Variety really does matter! Your dog's immune system will thank you, and the parasites won't.

The Bottom Line

I am not telling you to throw away your dog's flea and tick prevention. I am telling you to know what you're giving them and why. Your dog's age, size, health history, lifestyle, and your family situation all matter when making this decision. There is no one-size-fits-all answer. The answer is being more informed and knowing what you are putting into your dog's body. If you suspect your dog is having an adverse reaction, or are curious about all the potential side effects, here is a list of remedies to consider from a veterinarian.

What I do know is that informed decisions are always better than automatic ones. You are your dog's advocate, and you deserve the full picture. I wish someone had given it to me sooner.

If you want to learn more information about flea, tick, and heartworm prevention, I highly recommend the book, "The Forever Dog" by Dr. Karen Becker and Rodney Habib. It is a phenomenal resource.