How Do Dog Flea Treatments Work? Pills, Collars, And More Explained!

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There are many things I enjoy living in Minnesota, but the flea population isn’t one of them.

According to WebMD, Minnesota has one of the larger flea populations in the United States^[1].

One good thing is fleas aren’t very hearty when it comes to the cold, so it is less likely dogs will get fleas in the colder months. Flea season in Minnesota is traditionally April through November.

Unfortunately, flea season is getting worse because our winters aren’t as severe and our warmer seasons are getting longer.

Also, if a flea is attached to a host in the winter, the host keeps the flea warm enough to continue to survive and procreate.

So, what do we do when you live in an area flush with fleas?

In our house, we use a variety of preventatives in our home for a few different reasons.

My two youngest dogs take Bravecto Chews every three months, whereas my two older girls get Frontline applied every month.

The reason why we use different methods is due to the various health issues in our home.

Also, we have chosen Bravecto and Frontline because they also help the fight against ticks, which is also an issue in our area.

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Not sure if your dog is infested with fleas? We can help you figure that out!

How Do Flea Pills and Tablets Work?

Oral flea medications kill adult fleas, preventing them from laying eggs.

Most oral flea medications last at least 30 days and can be used to both prevent and treat flea infestations.

However, there is a treatment, Capstar, that’s solely used to manage flea infestations, and it only lasts 24 hours.

Most flea medications kill fleas by inhibiting aspects of their nervous systems, causing paralysis then death.

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Simparica (Sarolaner)

Active Ingredients – Sarolaner^[2]
How It Works – After your dog eats the Simparica chewable, the insecticide sarolaner enters the bloodstream. When fleas and ticks bite your pup, they will ingest the blood and die because sarolaner inhibits neurotransmitters such as GABA and glutamate^[3]. Fleas die within 3 hours.
How to Use It – The chewable pill is liver flavored so most dogs will readily eat it like a treat. If not, it can be wrapped or hidden in food.
How Long It Lasts – 35 days
Side Effects – Most common side effects are vomiting and diarrhea^[4]. In September of 2018, the FDA released a warning that stated isoxazoline class drugs might cause seizures and other neurological effects^[5]; Simparica contains this class of drug.
Prescription Needed? – Yes

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NexGard (Afoxolaner)

Active Ingredients – Afoxolaner
How It Works – Afoxolaner is effective after 4 hours of ingestion. It is an adulticide and kills adult fleas by blocking GABA-gated chloride channels before the fleas can lay eggs^[6].
How to Use It – Beef flavored chewable tablet
How Long It Lasts – 30 days
Side Effects – The most common side effects are vomiting, diarrhea, dry/flaky skin, lethargy, and lack of appetite^[7]. In September of 2018, the FDA released a warning that stated isoxazoline class drugs might cause seizures and other neurological effects; NexGard contains this class of drug.
Prescription Needed? Yes

Read our Nexgard Chewables review

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Bravecto (Fluralaner)

Active Ingredients – Fluralaner
How It Works – Kills adult fleas after two hours of consuming the chewable tablet by inhibiting ligand-gated chloride channels, thus shutting down the flea’s nervous system^[8].
How to Use It – Flavored chewable tablet
How Long it Lasts – 12 weeks
Side Effects – Common side effects are vomiting, decreased appetite, diarrhea, lethargy, polydipsia, and flatulence^[9]. In September of 2018, the FDA released a warning that stated isoxazoline class drugs might cause seizures and other neurological effects; Bravecto contains this class of drug.
Prescription Needed? Yes

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Capstar (Nitenpyram)

Active Ingredients – Nitenpyram
How It Works – Kills adult fleas within 30 minutes after being given. Nitenpyram is a neonicotinoid that inhibits postsynaptic nicotinic acetylcholine receptors^[10].
How to Use It – The tablet can be hidden in food or wrapped in a treat.
How Long It Lasts – 24 hours
Side Effects – Most frequent side effects are lethargy/depression, vomiting, itching, decreased appetite, diarrhea, hyperactivity, incoordination, trembling, seizures, panting, allergic reactions including hives, vocalization, salivation, fever, and nervousness^[11].
Prescription Needed? Yes

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How Do Flea Collars Work?

There are three main types of flea collars on the market.

The first kind of collar acts strictly as a repellent. The repellent is released in gas form from the collar.

The second type of flea collar kills fleas after the flea has bitten your dog.

The third collar kills fleas on contact before the flea bites your dog.

Seresto

Active Ingredients – Imidacloprid and Flumethrin
How It Works – Imidacloprid kills adult fleas and their larvae by wreaking havoc with their postsynaptic nicotinic acetylchlorine receptors^[12]. Flumethrin is a pyrethrin acts as a flea repellent by acting on sodium channels^[13].
How to Use It – Remove the collar from the bag. Make sure that the inside of the collar is free from any fragments from the plastic connectors. Guide the collar through the buckle and fasten around the dog’s neck. There should be able to put two fingers in between the collar and your dog’s neck. Cut off and discard the excess length of the collar, leaving about a one-inch tail. Finally, fasten the reflective clips to the collar; do not put clips on the area the collar length overlaps.
How Long It Lasts – 8 months
Side Effects – Most common side effects are itching, hair loss, and skin irritation^[14].
Prescription Needed? No

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Hartz Ultra Guard

Active Ingredients – Tetrachlorvinphos and Methoprene
How It Works – Tetrachlorvinphos kills adult fleas^[15]. Methoprene prevents normal molting, egg-laying, egg-hatching, and development from the immature phase to the adult phase^[16]. This collar also repels fleas.
How to use It – Remove the collar from the bag. Pull on both ends of the collar to activate the insecticide. Guide the collar through the buckle and fasten around the dog’s neck. There should be able to put two fingers in between the collar and your dog’s neck. Cut off the excess length of the collar, leaving about a one-inch tail.
How Long It Lasts – 7 months
Side Effects – Most typical side effects are skin irritation^[17]. More severe side effects include diarrhea, vomiting, difficulty breathing, small pupils, muscle tremor, weakness or falling over, and drooling^[18].
Prescription Needed? No

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Zodiac Flea & Tick Collar

Active Ingredients –Tetrachlorvinphos
How It Works – Tetrachlorvinphos is an organophosphate that kills fleas and controls larvae by inhibiting acetylcholinesterase, disrupting the flea’s CNS and GI system^[19]. The Zodiac collar also helps to repel fleas.
How to Use It – Remove the collar from the bag. Pull on both ends of the collar to activate the insecticide. Guide the collar through the buckle and fasten around the dog’s neck. There should be able to put two fingers in between the collar and your dog’s neck. Cut off the excess length of the collar, leaving about a one-inch tail.
How Long It Lasts – 7 months
Side Effects – Most likely side effects are skin irritation. More severe side effects include diarrhea, vomiting, difficulty breathing, small pupils, muscle tremor, weakness or falling over, and drooling.
Prescription Needed? No

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How Do Topical Flea Treatments Work?

Topical flea treatments are also called spot-on flea treatments.

Topical treatments consist of a liquid, usually applied between your dog’s shoulder blades. Applying the fluid between the shoulder blades prevents your dog from licking the treatment.

These treatments can be used to kill and sometimes even repel fleas.

Hartz Pet Defender Plus

Active Ingredients – Fipronil and Methoprene
How It Works – Fipronil works by blocking GABA-chloride and glutamate-chloride channels in the central nervous system in insects, ultimately killing the flea^[20]. Methoprene prevents normal molting, egg-laying, egg-hatching, and development from the immature phase to the adult phase by replacing growth hormones^[21].
How to Use It – Remove the tube from the packaging. Twist applicator tip to the right and at the same time push down to break the seal. Starting between your dog’s shoulder blades press the tube close to the skin. As you are squeezing, the tube move towards the tail, following the line of your dog’s spine.
How Long It Lasts – 1 month
Side Effects – Most typical side effect is skin irritation^[22].
Prescription Needed? No

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Vectra 3D (Ceva)

Active Ingredients – Dinotefuran, Pyriproxyfen, Permethrin
How It Works –Vectra 3D repels and kills fleas, as well as interrupting all of the flea’s life stages. Dinotefuran is a neonicotinoid and pyriproxyfen mimics growth hormones making it an insect growth regulator^[23], so Vectra 3D’s modes of action are all similar to other flea treatments above. Vectra starts working within 5 minutes after applying it.
How to Use It – Remove the tube from the packaging. Holding the tube upright, press down on the applicator tip until the two discs meet, breaking the internal seal. Starting at the base of the tail, part the hair and squeeze the tube, running along the line of the spine until you reach your dog’s shoulder blades.
How Long It Lasts – 1 month
Side Effects – Most typical side effects light redness, itching, or other signs of discomfort where the treatment was applied.
Prescription Needed? No

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Frontline

Active Ingredients – Fipronil and Methoprene
How It Works – Fipronil works by disrupting the normal function of the central nervous system in insects, ultimately killing the flea. Methoprene prevents normal molting, egg-laying, egg-hatching, and development from the immature phase to the adult phase. Methoprene prevents the insects from reproducing.
How to Use It – Remove the tube from the packaging. Twist applicator tip to the right and at the same time push down to break the seal. Part the hair between your dog’s shoulder blades and apply entire contents in the single area.
How Long It Lasts – 1 month
Side Effects – The most common side effect is temporary irritation.
Prescription Needed? No

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Vet’s Best Flea & Tick Spot-on

Active Ingredients – Clove Oil 7.5%, Thyme Oil 2.5%, Cinnamon Oil 2.5%
How It Works – Kills and repels fleas through the use of pesticide-free ingredients. These essential oils can suffocate the flea and also have neurotoxic mechanisms^[24].
How to Use It – Squeeze the tube at the point where the applicator and the tube meet; this will break the seal. Apply the liquid starting at the base of the neck and follow the line of the spine to the base of the tail.
How Long It Lasts – 1 month
Side Effects – The most common side effects are signs of sensitivity.
Prescription Needed? No

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How Do Flea Sprays Work?

Sprays work similarly to spot-on style treatments.

The spray kills fleas and prohibits the continued growth progression of larvae and eggs.

Vet’s Best Flea + Tick Spray for Dogs

Active Ingredients – Peppermint Oil 0.30%, Eugenol (from Clove plants) 0.70%, Sodium Lauryl Sulfate (plant-derived) 2.70%
How It Works – Peppermint oil and clove extract kill fleas and their eggs through physical and neurotoxic mechanisms, as mentioned above. SLS is a surfactant that aids in delivering the other ingredients to the inside of the flea^[25].
How to Use It – Spray on your dog’s coat directly, but avoid contact with the face, eyes, and genitals. However, be sure to spray the legs, stomach, and tail. Do not saturate your dog’s coat.
How Long It Lasts – The description states that it is long-lasting, but should not be applied more than twice in 24 hours.
Side Effects – The most common side effects are signs of sensitivity.
Prescription Needed? No

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Adams Plus Flea and Tick Spray

Active Ingredients – Etofenpox, Methoprene, Piperonyl Butoxide
How It Works – Kills fleas, eggs, and larvae and impedes the flea’s growth cycle. Etofenpox disrupts sodium channels^[26]. Methoprene replaces growth hormones. Piperonyl butoxide makes the other active ingredients more effective.
How to Use It – Shake well, then spray your dog’s entire body, including the tail, legs, and belly, but avoid their eyes, face, rectum, and genitals. With a cloth, gently apply to face around mouth, nose, and eyes. Spray until fully covered but not soaked.
How Long It Lasts – 2 months
Side Effects – Drooling may occur immediately after application.
Prescription Needed? No

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Frontline Spray

Active Ingredients – Fipronil 0.29%
How It Works – Fipronil works by disrupting the normal function of the central nervous system in insects by affecting the neurotransmitters GABA and glutamate, ultimately killing the flea
How to Use It – Apply until your dog’s coat is damp. Work spray in with gloved hand when applying to your dog’s coat. Avoid spraying the face, eyes, and mouth. To apply to face, spray your gloved hand then wipe the product on the dog’s face and ears while avoiding the eyes.
How Long it Lasts – 1 month
Side Effects –Sensitivities are rare, but still may happen after using Frontline Spray^[27].
Prescription Needed? No

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How Do Flea Shampoos Work?

Flea shampoos contain insecticides designed to kill fleas immediately and can also suffocate them.

Flea shampoos are used for when your dog has fleas or has been recently exposed to fleas.

These do not act as a potent preventative.

Richard’s Organics Flea & Tick Shampoo

Active Ingredients – Peppermint Oil, Eugenol (Clove Oil), Cedarwood Oil, Cinnamon Oil, Rosemary Oil, Sodium Lauryl Sulfate.
How It Works – Kills and repels fleas through mechanical (suffocation) and neurotoxic action.
How to Use It – Wet your dog’s coat down with water, then apply shampoo. Work the shampoo into your dog’s coat and allow to sit for five minutes before rinsing. Be careful not to let the shampoo to get into your dog’s eyes.
How Long It Lasts – The duration of the bath.
Side Effects – May cause skin irritation.

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Veterinary Formula Clinical Care Flea & Tick Shampoo

Active Ingredients – Pyrethrins, Piperonyl Butoxide, N-Octyl Bicyclopheptene Dicarboximide
How It Works – Kills fleas and soothes your dog’s skin from the irritations of the flea bites. Pyrethrins overexcite the flea’s neural pathways until the nerve cells are damaged, causing paralysis then death^[28]. The other active ingredients make the pyrethrins more effective.
How to Use It – Wear rubber gloves when shampooing your dog. Wet your dog’s coat down with water, then apply shampoo. Work the shampoo into your dog’s coat and allow it to sit for five minutes before rinsing. Be careful not to let the shampoo to get into your dog’s eyes.
How Long It Lasts – The duration of the bath, but should not be repeated for 7 days. Also, it may take up to 30 days to completely resolve a flea infestation.
Side Effects – Skin sensitivities may occur after use.

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Adams Flea & Tick Cleansing Shampoo

Active Ingredients – Pyrethrins 0.075%, Piperonyl Butoxide 0.750%, Pyriproxyfen 0.086%
How It Works – Pyrethrins kills flea and pyriproxyfen disrupts the growth cycle and prevents eggs from hatching for up to thirty days.
How to Use It – Wet your dog’s coat down with water, then apply 1-2 tablespoons of shampoo. Work the shampoo into your dog’s coat and allow to sit for five minutes before rinsing. Be careful not to let the shampoo to get into your dog’s eyes. Repeat every seven to ten days until the fleas are gone.
How Long It Lasts – Up to 30 days for preventing flea eggs from hatching.
Side Effects – Skin sensitivities may occur after use.

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Which One to Use and When

There are a variety of different flea products on the market because there isn’t just one flea solution that will work with every situation.

Factors like your dog’s age, health, and activity level all play into which flea product would be best for your situation.

Scenario 1: Your Dog LOVES the Water

Harts ultra guard water proof resistant flea tick collar — Hartz does make a water-resistant flea collar, though it won’t be as water resistant as other options

If your dog enjoys swimming and does so frequently, a flea collar may not be the best choice.

Many flea collars state that exposure to water is not recommended more than once a month.

In this situation, it would be best to consider using an oral medication or spot-on type treatment.

Oral medications do not have any water restrictions.

Topical treatments do not recommend exposure to water for 48 hours after application, but then do not have any water restrictions for the balance of the month.

Scenario 2: You Have a New Puppy and Want to Avoid Fleas

Flea products have different age ratings, so if you just picked up an eight-week-old puppy, then the best option is topical treatment.

Most spot-on treatments are safe to use with puppies eight weeks old and up.

Scenario 3: You Live in an Area That Fleas Aren’t a Problem, but Plan on Visiting an Area with a High Flea Population

Because your pet doesn’t require long term treatment, a spot-on or spray-on treatment would be best.

Just be sure to apply it in advance of traveling so that it has time to absorb into your dog’s skin and bloodstream.

Scenario 4: Your Pooch Has Fleas

Unfortunately, fleas happen.

Pet Fusion dog bed flea infestation spray protect furniture — Fleas love dog beds. Use flea control sprays to keep them away!

One time, I picked up a foster dog from animal control and she had fleas.

The first thing I did was to call my vet and get Capstar. Capstar works quickly and effectively to get rid of fleas.

The second thing I did after giving my foster Capstar was to apply Frontline.

After an hour, I felt safe to bring her home, but I did use flea spray on the dog’s bedding in my car and my house.

Using all three products avoided a flea infestation in my home while at the same time ridding my foster of her pesky fleas.

Side Note When Using Multiple Flea Products

Some products are safe to use together.

However, it’s always safest to consult your vet before combining products since overexposure to pesticides can cause toxicity issues in your dog.

Final Thoughts

Vet's Best flea tick yard kennel spray prevent flea infestations — Don’t forget to get a yard spray to protect your dog from bringing fleas in from outside!

If I could give any pet parent one piece of advice when it comes to fleas, it would be to use a flea preventative.

Avoiding a flea problem is, by far, the easiest way to deal with flea issues. Flea preventatives might seem pricey, but in truth, they are a lot cheaper than dealing with a flea infestation in your home!

I know there are many flea products on the market which can make it challenging to know which product would work best.

Hopefully, I was able to get you started in the right direction and help you narrow down the best solution for you and your dog.

How Does Dog Flea Treatment Work? Pills, Sprays, Shampoos, Collars, and Spot-On (Topical) Explained