How Long Does Flea Treatment Take to Work? Pills, Tablets, Collars, and Drops (Topical)

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Any dog that spends enough time outside or around other dogs will come into contact with fleas at some point.

It’s no fault of the owner, since fleas are too tiny to see while your dog is running around the dog park or enjoying a walk.

When Maggie gets fleas in the future, I know I’ll want to get her the best help as soon as possible.

For me, that meant I needed to research and find out the different kinds of flea treatments and how long they take to work.

Make your dog comfortable and happy the next time they have fleas by reading about how long different flea treatments take to work.

Whatever treatment you choose, your dog will be better off once you’re more informed.

How Long Do Flea Pills Take to Start Working?

Giving your dog a veterinary recommended flea pill is great, but you can’t exactly see it in action.

So, how long does it take to start working?

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Small dog owners may think that the pill will kick in faster in tiny dogs, just like big dog owners can think it’ll take longer to protect their pup.

The truth is that it doesn’t matter what size your dog is, as long as they’re getting the right dosage for their weight[1].

The vet will already decide that before you give your dog the flea pill.

Based on Activity Level

Dogs that are more active and spend more time outside will still be protected by the flea pill, even if they run out to the backyard right after taking their dose.

Flea pill ingredients are meant to last the entire month or even the year, depending on the brand you buy.

No amount of physical activity will work the ingredients out of your dog’s system.

For Fleas to Die

After your dog swallows the flea pill, most pills will kill fleas after 30 minutes[2].

After four hours, there should be no more sign of live fleas on your dog.

For Dog to Stop Scratching/ItchingPuppy scratching fleas itch relief how long until dog stops

Dogs scratch at fleas because the fleas are biting their skin, so after the flea pill successfully kills those fleas, the scratching and itching should stop.

Give your dog thirty minutes to an hour for the scratching to calm down.

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For Prevention to Start

Flea prevention starts as soon as your dog takes their flea pill.

It’ll last as long as is indicated on the pill box, which will be different for different brands.

How Long Do Flea Collars Take to Start Working?

Flea collars are another option for dog owners and it’s one that many choose because it’s so budget friendly.

Based on Dog Size

The size of the dog doesn’t really matter when it comes to the flea collar.

The only issue may be the thickness of the coat, which is seen mostly in bigger dogs.

Thick coats make it harder for the collar to spread its insecticide, but it will still work for all breeds.

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Dogs that have any level of activity can use the flea collar, but you may want to take it off while they swim[3].

Flea collars can take a walk in the rain or a run through the sprinkler, but if they’re dunked for long periods of time, the insecticide will be released into the water and not necessarily onto your dog.

For Fleas to Die

Flea collars begin working immediately, but may take a few hours to kill all the fleas on your dog.

For Dog to Stop Scratching/Itching

Your dog’s itching and scratching should stop as the fleas die off, which may take a few hours or overnight with a flea collar.

For Prevention to Start

Make sure when you purchase a flea collar that it both repels and kills fleas.

Some are designed to do either one or the other.

Flea repelling collars will start working right away, just like collars that kill other pests.

How Long Do Topical Flea Drops Take to Start Working?

Topical flea drops are a time tested way to take care of flea infestations, so here’s what you need to know about how they work.

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Flea drops are bought depending on the weight of your dog, so the dosage is pre-adjusted accordingly.

The size of your dog will only affect the dosage they need, not the effectiveness of the drops.

Based on Activity Level

Active dogs can use flea drops just like non-active dogs can.

Flea drops are oil based, so the treatment should stay on if your dog gets splashed.

Read the instructions for your dog’s flea drops carefully before applying, since it may be a few hours before they can go swimming or get a bath after their treatment.

For Fleas to Die

Flea drops need time to soak into the sebaceous system, but fleas should start to die after an hour or two.

For Dog to Stop Scratching/Itching

Your dog’s scratching and itching should subside as fleas die, which may take a few hours after application.

For Prevention to Start

Prevention starts as soon as the flea drops soak into your dog’s skin.

The prevention will be more effective after treatment if it isn’t touched or washed until it’s dried out.

How Long Do Flea Sprays Take to Start Working?

Flea sprays are another cost effective way to control a flea infestation, but how quickly do they kill fleas?

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The size of the dog doesn’t really matter for flea sprays.

The only concern is that the dog is over 12 weeks old.

Based on Activity Level

Flea sprays work on both outdoor and indoor dogs, so activity level isn’t an issue.

In fact, running around during a game of fetch might be a good idea, since it’ll help the flea spray dry.

For Fleas to Die

Fleas will start dying as soon as the flea spray product reaches your dog’s skin.

Most will die after one application, but a second or third application is fine after 2-4 hours.

For Dog to Stop Scratching/Itching

Your dog may have minor scratching as the flea spray dries, but that’s normal.

The scratching and itching will go away with one or two applications after the spray dries.

For Prevention to Start

Flea sprays are mostly meant as a means to kill fleas, not prevent them.

However, if you find a brand that does both, the prevention should start after the application is complete and rubbed into the skin.

How Long Do Flea Shampoos Take to Start Working?

Your first instinct may be to bathe your dog with a flea shampoo once you discover the fleas, which is a great option to kill fleas quickly.Hartr Ultra Guard flea tick shampoo when does it kill fleas and for how long

Based on Dog Size

Dogs of all sizes can be bathed with flea shampoo, without worrying about using too much or too little.

Based on Activity Level

Active dogs can also use flea shampoos, although they may want to stay indoors and away from public dog spaces after they’re done with their bath to give it more time to work.

For Fleas to Die

Flea shampoos begin killing fleas upon immediate contact.

They’re a powerful insecticide that’s completely safe for your dog’s skin.

For Dog to Stop Scratching/Itching

After you bathe your dog, many fleas should get washed down the drain.

The scratching and itching will especially stop if a flea comb is used after a bath to get even more fleas and eggs out of your dog’s coat.

For Prevention to Start

Flea shampoos are meant to take care of an infestation, not prevent one.

The longest they’ll prevent fleas is for the next few days after a bath, but then the product will wear off.

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It’s a good idea to treat not only your dog but their kennel and your yard as well


There are a ton of different ways to take care of fleas, and they all have different features that dog owners should be aware of.

Most will begin killing fleas right away and may take some time to fully work.

Always be sure to read the box or container of the product you buy so you know how to use it the right way.


How Long Does it Take for Frontline to Kill Fleas?

Frontline will begin working immediately and should kill all fleas on your dog within 12 hours[4].

How Long Does it Take for a Seresto Flea Collar to Work?

The Seresto flea collar takes 24 hours to kill all fleas on your dog, then should kill re-infesting fleas during the following two hours[5].

How Long Does it Take for a PetArmor to Work?

PetArmor will work during the first 12 hours, but may take a full 48 hours to successfully kill all fleas[6].

How Long Does it Take for Advantage Flea Medicine to Work?

Advantage starts killing fleas for 12 hours after application, with an additional two hours of effectiveness to protect against re-infestation[7].



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