Each year, pet owners spend more than 379 million dollars on a myriad of flea medications for their pets. Brookfield takes a look at some of the most popular brands in stores and which ones are the safest and best at keeping your pet free of fleas and other external parasites.


First, A Word About Itchy Pets


If you’re reading this article because your pet is scratching, don’t necessarily assume that the itching is related to fleas.  Itchiness in pets is one of the most common ailments veterinarians are asked to treat. Though every veterinarian will rule out fleas as a cause of your pet’s itchiness, only about 2 out of every 10 itchy dogs or cats actually has fleas. Itchiness in pets is most frequently caused by food or environmental allergies.  In these cases, flea medication won’t stop your pet from scratching.


Second, A Lesson About Fleas


In order to pick the best flea product for your dog or cat, you have to understand a little about the flea life cycle since the success of any flea product is usually tied to how it kills adult fleas and stops further infection.


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Flea Life Cycle


Both male and female fleas mature sexually after biting your pet and taking a blood meal, but females are the more voracious eaters of the two.  After feeding, females lay eggs on your pets skin or fur which fall to the floor of your home or into the cracks and crevices of your pet’s bedding (or yours if you share a sleeping spot).  Eggs hatch into larvae which feed on anything organic in the environment including the feces of their parents.  Larvae complete their maturation process as pupae in cocoons and emerge as adults which jump back onto your pet to commence feeding and start the whole cycle again. If you’d like to read more on the life cycle of fleas and treating infestations, read our article on the topic, Treating Fleas.


Seeing Fleas On Your Pet


Unless your pet has a substantial infestation, you probably won’t see fleas on him or her. Ninety-five percent of any flea population exists off your pet, as adults living on the floor of your home, or as flea eggs, larvae, and pupae in your carpet, in the cracks of your floor boards, in your pet’s bedding, and in the crevices of your furniture cushions. More common is to see the flea feces on your pet, also called flea dirt. Flea dirt looks like black pepper at the base of your pet’s fur or on his or her skin.  Distinguish flea feces from regular dirty by smearing some onto a moist paper towel. Flea dirt will stain the wet paper towel a rust-colored red. Look for flea dirt near the spots fleas are more likely to feed: on your pet’s rump, face and neck, and belly.


How Flea Medications Work


The best flea products are qualified by their safety, their ability to kill existing adult fleas, to break the reproductive cycle of fleas, to repel fleas, or all of the above. We’ll get to specific flea products and how they work in a moment, but first, a little on the active ingredients you are likely to find in flea products.



Fipronil is a insecticide found in many topical flea products. It binds to the nerve endings of insects to kill them. Fipronil is toxic to fish and some birds and in large quantities toxic to animals and humans. Apply products that contain fipronil at the base of your pet’s neck where he or she can’t lick it off. Always wash your hands after applying a fipronil-based product.


S-methoprene is a hormone that acts as a growth regulator and prevents flea larvae and pupae from developing into adults. S-methoprene is considered to be relatively safe in the dosages found in all major, American-produced, flea and tick products.


Permethrin, and chemicals like it, can be found in most of common flea products sold in big box stores.  It is a neurotoxin that rapidly kills adult fleas, but is toxic to cats and has a noteworthy track record of causing adverse reactions in dogs, especially when overdosed. Humans can suffer skin irritation or skin tingling after coming in direct contact with permethrin. It is highly toxic to fish.  Animals and humans that accidentally ingest permethrin can suffer seizures, muscle tremors, vomiting, nausea, and abdominal pain.


Imidacloprid is a neurotoxin related to nicotine. Insects that contact the substance experience paralysis and then death. If applied topically, it is safe for animals, but can be toxic if ingested.

Isoxazoline Class Chemicals

Many oral and some topical flea medications contain chemicals in the isoxazoline class, namely fluralaner, afloxalaner, lotilaner, and sarolaner. The FDA has approved flea products containing these active ingredients, but issued a warning in 2019 stating that some dogs and cats had adverse reactions including tremors and seizures. Isoxazoline class drugs are absorbed systemically by pets. Fleas and ticks are killed when they take a blood meal.


Never Mix and Match


Most of the adverse flea medication reactions we see are ones caused when pet owners use a dog product to treat a cat.  Another significant cause is the over application of products. Pet owners will treat a pet for fleas, but continue to see fleas on the pet after application of the product, so they reapply more product.  Big mistake.


Seeing fleas on a pet after treatment with a flea product is usually because there are flea eggs and larva in the house that continue to mature and jump on your pet and feed. Another cause is that the flea medication excites the nervous system of the flea before it dies, causing it to be more active and consequently easier to spot. Flea products that include an insect growth regulator like s-methoprene eventually kill the other life stages of the flea (except the pupa stage), but it takes time.  If your pet has a confirmed flea infestation, you have to treat both the pet and the pet’s living environment.  Use this link to learn how to get rid of fleas in your house.


The Best Flea and Tick Products For Dogs And Cats

Simparica Trio


Simparica Trio is a once-a-month chewable tab that protects your dog against fleas, ticks, heartworm disease, and some intestinal parasites. It can be used to treat dogs 8 weeks of age or older and weighing at least 3 lbs. Because it contains a medication to protect against heartworm disease (moxidectin), it can only be purchased with a prescription from a veterinarian. In studies, the drug has proven to be highly protective against Lyme disease. This drug does not repel fleas and ticks, but kills both quickly should they take a blood meal. This drug earns a 5 star rating from our veterinarians for safety, efficacy, and ease of administration.



NexGard is another flea and tick preventative that contains an active ingredient from the isoxazolene class of insecticides.  Very safe, this  medication comes in a flavorful chew that should be administered monthly.  It kills 4 kinds of ticks and fleas.  Due to the speed with which it kills ticks, it can be used as an effective deterrent against Lyme disease.

Revolution Plus


Though this product is also made for dogs, Revolution is our go-to flea and heartworm preventative for cats. Two active ingredients, selamectin and sarolaner protect your cat against ear mites, some intestinal parasites, heartworm disease, fleas and ticks. It also kills any flea larva or flea eggs that are in your pet’s environment. Because of its safety and efficacy, we recommend it for all cats, even those that spend most of their time indoors. Revolution is a topical solution that is administered once monthly on the skin at the base of your cat’s neck.

Frontline Plus


Probably the most recognizable of all the flea medications shown here, Frontline Plus is a once-a-month topical solution that is applied to the back of your pet’s neck to effectively protect against fleas and ticks. The medication contains two active ingredients, fipronil, to kill adult fleas, and s-methoprene, to kill larvae and eggs in the pet’s environment.  Because of its tick killing effectiveness, the medication is considered an effective deterrent against Lyme disease. The product is manufactured for both dogs and cats.

Seresto Collar


We included the Seresto collar on our list because of its ability to both kill and repel fleas and ticks. It active ingredients are imidacloprid and flumathrin.  The product has a wide spectrum, killing adult and larval stage fleas, adult ticks, chewing lice, and sarcoptic mange. The collar can be purchased over-the-counter and is effective for 8 months.  There is also a version manufactured for cats.

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