Flea and ticks are pests I think we all can all agree we can do without, they’re creepy, crawly and they spread diseases. Unfortunately, ticks are part of our lives, and chances are you’ve seen a flea or tick in your lifetime, especially if you have a dog.

No one wants to find a tick on their dog, so we listen to our vet and purchase the flea and tick products based on their recommendations. Frontline Plus, K9 Advantix II, NexGard, Seresto are all commonly available from your vet, online or in the pet stores.

But did you know the active ingredients in all of these products are pesticides? Yes, you read that correct, you are putting poison on your dog! Yikes, scary right?

How can these companies get away with marketing a poison to pet owners? They all say the amount is slow-releasing in small amounts and are perfectly safe for your dog. Really? Would you put pesticides on yourself or your kids?

WARNING! The Truth About Flea and Tick Medications

UPDATE: 9/20/18 from the FDA: Animal Drug Safety Communication: FDA Alerts Pet Owners and Veterinarians About Potential for Neurologic Adverse Events Associated with Certain Flea and Tick Products

On the list of products the FDA is warning us about are Bravecto, Credelio, Nexgard and Simparica. Some pets have experienced adverse events such as muscle tremors, ataxia, and seizures.

Safety Warning for Flea and Tick Meds

Even the K9 Advantix box warns that it is hazardous to humans and fatal to cats! Here is a photo I took of the box of K9 Advantix I bought last year. More than half of the box are hazard warnings! Notice how they attempt to distract you from those warnings by putting the benefits in red. Yikes, do I really want to put this on my dog?

K9 Advantix Warnings
Click to enlarge and read!

If you Google the brand you use and side effects, you can read story after story on how dogs have had severe reactions to this stuff. Some as simple as skin irritation but many as serious as seizures or death.

Now, of course, there are many dogs that don’t have any visible side effects, but how do we really know that they aren’t experiencing any long-term medical issues from this pesticide we are intentionally exposing them to?

What Are the Active Ingredients in Flea and Tick Products?

We’ve used both Frontline Plus and K9 Advantix on our dogs. I’m embarrassed to admit, I never looked at the back of the boxes until a few years ago. After reading something online, I started researching and it didn’t take long for me to realize this stuff is slowly killing our dogs.

Even the Humane Society of the United States warns us about the use of these chemicals on our dogs! “Before you use any of these products on your pets, it is critical to read their labels and consult with your veterinarian. They may contain ingredients that could harm pets and people.”

I’ve researched each of the top-selling flea and tick products. Found their active ingredient list from their website and put it all together here for you to make your own informed decision.

Scary fact: I found all the ingredients listed on these flea and tick medications on the National Pesticide Information Center. Source: National Pesticide Information Center

Frontline Plus


Ingredients: Fipronil, (S)-methoprene

Fipronil is a broad use insecticide that belongs to the phenylpyrazole chemical family. Fipronil is white powder with a moldy odor, used to control ants, beetles, cockroaches, fleas, ticks, termites, mole crickets, thrips, rootworms, weevils, and other insects.

Methoprene is used against insects. It comes in two different forms called s-methoprene and r-methoprene, and s-methoprene is the one that behaves like an important hormone in insects. It can be used against fleas, flies, moths, beetles, and other insects.

K9 Advantix II


Ingredients: Imidacloprid, Permethrin, Pyriproxyfen

Imidacloprid is an insecticide that was made to mimic nicotine. Nicotine is naturally found in many plants, including tobacco, and is toxic to insects. Imidacloprid is used to control sucking insects, termites, some soil insects, and fleas on pets.

Permethrin is an insecticide in the pyrethroid family. Pyrethroids are synthetic chemicals that act like natural extracts from the chrysanthemum flower. Permethrin is used in a number of ways to control insects. Products containing permethrin may be used in public health mosquito control programs. They may be used on food and feed crops, on ornamental lawns, on livestock and pets, in structures and buildings, and on clothing. Permethrin may also be used in places where food is handled, such as restaurants.

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Pyriproxyfen mimics a natural hormone in insects and disrupts their growth. It is a type of insect growth regulator that affects mostly young insects and eggs. Pyriproxyfen affects many types of insects, including fleas, cockroaches, ticks, ants, carpet beetles, and mosquitoes.



Ingredients: Afoxolaner has the chemical composition 1-Naphthalenecarboxamide, 4-[5- [3-chloro-5-(trifluoromethyl)-phenyl]-4, 5-dihydro-5-(trifluoromethyl)-3-isoxazolyl]-N-[2-oxo-2-[(2,2,2-trifluoroethyl)amino]ethyl.

From what I can tell Afoxolaner was created specifically for use in NexGard? So that is why they have the breakdown of what the composition of the chemicals is, the only chemical I could find is Naphthalene carboxamide.

Naphthalene is an aromatic hydrocarbon found in coal car or crude oil. Naphthalene is used in the manufacture of plastics, resins, fuels, and dyes. It is also used as a fumigant insecticide that works by turning directly from a solid into a toxic vapor. This process is called sublimation. Most products containing naphthalene in the U.S. are used to control clothes moths in airtight containers.



Ingredients: Imidacloprid, Flumethrin

Imidacloprid is an insecticide that was made to mimic nicotine. Nicotine is naturally found in many plants, including tobacco, and is toxic to insects. Imidacloprid is used to control sucking insects, termites, some soil insects, and fleas on pets.

There it is in black and white, each one of these popular flea and tick products that are recommended to use on our dogs contains insecticides. Do you still feel it’s okay to protect your dog with these chemicals?

If you are wondering if heartworm preventative is safe, same rules apply. Check out The Truth About Heartworms By Only Natural Pet.

Side Effects of Flea and Tick Medication

  • Vomiting
  • Diarrhea
  • Lethargy
  • Weakness
  • Staggering
  • Disorientation
  • Hypothermia
  • Abdominal pain
  • Light or severe depression
  • Allergic reactions, such as rashes and itching

Is It Possible to Protect Your Dog from Fleas and Ticks with Natural Ingredients?

I will admit, I’m scared to NOT protect my dogs from fleas and ticks. Our foster dog, Taylor had Lyme disease, which is contracted from being bit by an infected tick. And now that we will be living in a rural area that is known to have ticks, I need to make sure I protect my dogs and family.

So I began searching for natural flea and tick prevention for our dogs. From homemade flea and tick prevention with essential oils to natural products available to purchase online.

After testing several natural options, I now use Only Natural Pet products to protect all of our dogs. With a combination of the tick tag, garlic tabs and spray, we haven’t seen a tick on the dogs for several years.

Read more at Natural Tick and Flea Prevention for Dogs

So How Can We Protect Our Dogs from Fleas and Ticks?

Should you continue using Frontline Plus or K9 Advantix? I don’t have the right answer for you. You aren’t a bad dog parent if you decide to use these products, we all need to make our own decisions and do what is best for our dogs. No judgement from me. But now that you know the facts, I’d love to hear what you decide to use to protect your dog from fleas and ticks. Will you continue to use the pesticide products, or try something natural?

Please comment below with what works for you and your dog, it will help others in the Rescue Dogs 101 community to make an informed decision.

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About the Author

Debi McKee

Debi McKee is the expert behind Rescue Dogs 101 where she guides you in your journey of adopting and raising a rescue dog every step of the way. She is a mom of 3 human kids and 4 dogs and volunteers for a local dog rescue and Humane Society. Click here for more about Debi and her passion for helping you and your dog.

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  1. We recently tried the K9 Preventa Flea/Tick treatment on our dogs. The usual treatment we use was not available. This was approximately 2 weeks ago. Since then, our one small dog has been vomiting off and on. Since the application. We tried to rule out all other alternatives of cause. But it started the night after its application. I am starting to wonder if this is the cause. Her episodes have been off and on. She behaves completed normal, except that she is having food adversions (extremely unlike her) and random vomiting episodes. I have no idea if this is the cause or not. But we have looked through all other options at this point.

    1. I’m so sorry your pup is experiencing these side effects. I would talk with your vet to rule out any other health issue. And then contact the manufacturer so they know about the reaction. Hope she feels better soon!

  2. I'm so torn and afraid. My 9 year old Chihuahua mix is a few days overdue for Frontline plus. I just relocated to New England. Lots of ticks and Lyme.My vet said to keep up with it and he gets upset when patients show him internet articles. He said seeing a dog with Lyme is horrible. My daughter's pit bull got Lyme and oh,my gosh,was he ill.She depleted her savings for his treatment. Her other rescue had heartworm. That being said, I realize it's a neurotoxin. I live in the middle of the woods.I only want what's best for my best friend.

  3. I am sorry to post this horrible story but my beautiful 14 year old cocker spaniel went through a horrible death within 12 days of using K9 Advantix II. It didn’t occur to me it was the pesticides in the topical flea and tick prevention until 2 weeks after she was put down when I read something online. She acted confused starring at walls, trying to hide, getting tangled in wires and under chairs and she fell down 13 basement steps in the middle of the night. Took her to the vet she acted ok and had a good check up but as soon as I got her home she had one seizure drove to the hospital where she convulsed violently all the way there. They medicated her and kept her over night and called us in the next morning and put her down because there was no improvement. It pains me to relive that night and I feel so helpless because I know dogs have almost no rites and nobody can do anything for her ordeal.

  4. People should be aware that the ingredient DMDM hydantoin is an antimicrobial formaldehyde releaser preservative with the trade name Glydant. DMDM hydantoin is an organic compound belonging to a class of compounds known as hydantoins. It is used in the cosmetics industry and found in products like shampoos, hair conditioners, hair gels, and skin care products.

    Do some research and decide if this ingredient is suited to what you want the product to accomplish. It is used in so called natural products.

  5. im between a rock and a hard place, i have 6 large hairy dogs and moving to a presently heavily tic infested part of the country..we had 2 cases of lymes there last summer, and thats when the tics arent that bad, fall and spring are the worst….we go as natural as we can in all things, dogs fed raw, but, moving out east presents its own set of difficulties…i pulled 10 tics of one of my dogs last fall 🙁 and the same amount on some of the others…but i wouldnt put advantic or frontline on myself so what do we do

    1. Sometimes we are faced with the choice between the chemical treatments or an even worse fate of lymes or other diseases. If you’ve tried all the natural treatments and they don’t work, then unfortunately you may need to resort to the chemical options. Try layering the natural treatments, the more “shields” the better. And also consider that a tick needs to attach before it can infect your dog. SO if you have the time to groom and check each dog after being outside then… well that’s a lot to ask I know. There have been a few times I “almost” reverted back to frontline, but then I up my natural defense game. But then again I don’t think we are not in a high infested area as you may be.

  6. Hi! Thank you for posting this article. I've read all about adverse reactions to many pet meds and pest prevention but haven't found natural products to prevent as of yet. My 3 dogs have been taking the brewers yeast tabs for 2 months, they still get fleas but I do believe it's less than last summer. We use kin & kind shampoo and it works but it kills what's already there. So, I'm looking at the tags you mentioned for sure but the spray you use, is it for the home or the yard?

  7. I had 2 dogs die from
    Seizures within 6 months of each other. I’m convinced it’s this flea and tick treatment, I used k9 advantix 2, on them
    Both and they both died the exact same way. No previous health issues !!! I made the manufacturer’s aware of this and noted I would make it a mission to spread the word their products are killing our pets !!!!!

  8. I am concerned about using tick prevention medicine on my Yorkie. She has allergies. I use advantage with no real problem but vet said that is not for ticks. Recently she contracted anaplasma from an infected tick. Now with spring coming i am afraid of what to use. She is on doxycycline for a month. What natural products are there and do they really work. I live in a wooded area. Thank you

  9. I came here for real information and immediately jumped off board at “pesticides are poisons on your dog, AHHHHHHH!” segment. Of course they’re pesticides. They kill pests. That’s The fing point. You know what else are pesticides? Many essential oils… And Neem oil, and soaps, and a whole bunch of other things that are not dog-icides.

  10. Always follow your vet’s recommendations and the label instructions when administering flea and tick preventives. Never use a dog product on a cat.

    1. Many vets bet kick-backs for promoting a certain product. I vote pushes Credelio, which contains lotilaner. The FDA actually came and warned about that group of chemicals' potential neurological side-effects. You know if the FDA says something is bad, it must be. Look at all the bad stuff they let slide. Anyway, Not all vets, I believe, are out for the betterment of your pets. Some, just like people docs, are in it for the $$$. Do your own research and be smart.

  11. I have 2 Cavaliers, I have tried natural remedies for fleas, nothing is working, and I hate to see them scratching. They have soresto collars and even they are not working! I have just been and bought Nexgard, I am worried about giving it to them, I have researched but at the moment I feel there is no other option. I live in southern Spain

    1. I used nexgard on my schnauzer for 1 yr and then she started having seizures. Although she has been off of it for 3 yrs she still has seizures from time to time. I would not do it personally…just my opinion

  12. I applied Advantix on both of my 1 year old Yorkies today. One seemed to do fine but I noticed one had his tongue hanging out, then he threw up. He just didn’t act right so I took him to the sink and washed him. After throwing up two more times and shaking for several hours he seems to be better. I washed the Advantix off of the other one too. Didn’t want to chance his getting sick also.

  13. I have been looking for something natural and safe to repel and protect my Tasha from fleas, ticks and mosquito during our nature walks or sitting in the back yard. She likes to cool off in the lake during our nature walks so I have to reapply time and time again. UGH.

  14. Thanks for all information on flea and tick choices all seem bad if you ever find something that works without poisoning my dog would love to know .

    Thanks Terry

  15. I had used one of the oral flea and tick treatments for my 2 dogs and 2 cats. With in days one of my cats went into irreversible kidney failure and was euthanized. Currently I started using Advantix on my dog. First application was fine, I just applied the second month application yesterday afternoon. This morning she is showing symptoms of hind end paralysis. I’ve washed her in dish soap and going to vet. I’m praying she will be ok..

    1. Its says on the Advantix box not to use around cats ! Advantix can only be used on dogs and should not be used around cats. It is literally poison for them.

  16. We used frontline years ago and it seemed work, then we switched to flea stop that goes in the water. At some point we quit that and used nothing g. After 2 seasons of flea infestation (finally got rid of in house with diatomaceous earth) we started using advantix (frontline failed this time). As much as I dislike putting this on our dog, I haven’t wanted to chance another infestation, as it was a pain. We have bennusing a few months and after application yesterday our dog could get up for a few minutes. It scared us. I may try something else again. It was maybe 20 min after application. Luckily she seems fine now. She is 15 years old, so. I hate to compromise her system again.

    1. oh my Ashley, I’m so sorry to hear this happened to your dog. I’d talk to your vet to let them know what happened at the very least. We don’t struggle with fleas as much as we do with ticks here in WI. I can only imagine the struggle with the fleas is horrendous.

  17. Upon recommendation from our previous vet, we administered Advantix II to our Mastador. Within a day, he could barely walk. His hind legs were weak and wouldn’t support him. Months later, after thousands of dollars spent on some great specialists, we finally were able to get him back on his feet. Bayer describes this product as a “drug” when in fact, it is primarily insecticides. Their packaging instructs you to wear gloves when applying the product. Any product that requires me to wear gloves, will not be applied to my dog.

    1. I am so sorry to hear about your experience. It’s unfortunate that these stories exist and so scary. I’m glad your dog is okay now. We’ve been using the All Natural Pet tag with great success. No ticks since I started using it in April!

  18. Hi Debi
    It’s very disappointing to read this article.
    While every medication has the potential to cause an adverse reaction, what you are implying here is that these products are dangerous and that just isn’t true.

    Vets recommend these products because they save lives.

    Many of the issues that you note are not due to the product, it’s that whole correlation vs causation problem.

    I plead with you to remove the unfounded and incorrect advice and replace it with facts. You will do more to help rescue dogs this way.

    All the best
    Dr Leigh

    1. Well we will have to agree to disagree. The article is full of facts backed by the FDA warning and the Humane Society. I have not suggested anyone stop using the medications if they feel that is right for them. But I will never use these chemicals on my dogs ever again. I have found a natural way to keep fleas and ticks off my dogs without the dangers of these chemicals. Just because they are approved by your vet, does not make them good for our dogs.

    2. many dogs have died from these pesticides. You are the one that is wrong Dr. do your research! Mine had severe reaction and had to be put down. Many many others experienced issues the first day after application. How much does Merck or Bayer pay you to offer these?

      1. I’m so sorry Shirley to hear about your dog. So sad that as pet parents we are pushed these products by vets we are suppose to trust. At the very least they should be educating their patients before selling them.

    3. If there is no danger, why do the product warnings state for humans not to come into contact of the medication through their skin? If it's not safe for my skin, a 150 lb. adult, why would it be safe for my 9 lb dog?

    4. Dr. Leigh, perhaps read this article: https://ivcjournal.com/isoxazoline-flea-and-tick/ and watch this segment:https://www.cbsnews.com/news/seresto-collar-deaths-symptoms-collar-should-be-recalled-fleas-ticks-report-says/

      The FDA approves all sorts of things that are harmful. Many vets are motivated by money and receive kickbacks from prescribing certain products.

      This article is factual, I've done my research. And there are too many reports of adverse effects than can only be attributed to these pesticides.

  19. K9 Advantix II- Serious Adverse Effects on Havanese
    We have a 13 lb. 7 y.o. Havanese on which we have regularly used Frontline as a measure against black-legged ticks, and other insects, since her first bithday. As Chair of the Board of Health and actively involved in Lyme Disease and other Tick-Borne Disease counter-measures, prevention of infection, and promotion of information, I have actively promoted topical medications for household dogs. In the past year, both the MA DPH and the Cape Cod Extension & Barnstable Cty Health expert, Larry Dapsis, has recommended one oral and one topical product to replace Frontline, with K9 Advantix II being the topical. We purchased K9 Advantix and yesterday applied the product to our Havanese. Within 2 hours she showed agitation with indications of intense itchiness (as she rolled around on every surface she could find), parasthesia and hind quarter muscle spasms or tremors.

    Our Board actively promotes the use of Permethrin (an anti-insect synthetic equivalent to the chrysantemum-based pyrethrin) as applied to clothing to prevent ticks and other insects from climbing onto shoes and pant legs.

    Apparently, even the “Medium Dog” dosage for a 13 lb. dog was far too intense or effected otherwise as it caused intense adverse effects.

    1. You are welcome Nuii. We used Frontline for years. Everyone needs to make the right decision for their situation and dog. I know the natural options aren’t as strong, so some that live in high infested areas, need to consider that’s best for the dog.

  20. Great article! Also, there are many others way to get rid of fleas on dog. like using a flea comb, Apple Cider Vinegar, Planting flea repellant plants, Fogging house occasionally etc.

    1. Doterra peppermint is the purest and there are dilution charts available if you ask your wellness advocate in Doterra

  21. I use peppermint, I put it in a spray bottle it kills fleas on contact. The dogs may not like the cooling effect that it has on them, but it only last for a few minutes. But it’s better than all the other choices. Plus it makes the HOUSE smell great !

    1. That’s great, I heard peppermint is a great option. Just make sure it is diluted correctly otherwise it could become an irritant to your dog. So glad you found something that works for you and your dog!

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