How Long Does It Take for Flea Medicine to Work on Cats?

by K Marie Alto October 13, 2022 12 min read

How Long Does It Take for Flea Medicine to Work on Cats?

Fleas 🪲 are one of the most common and unpredictable parasites that spring up around household pets.

They show up seemingly at random, and though they're a lot more common with indoor/outdoor pets, they can even infect an indoor-only cat and leave you wondering how it happened.

How does it happen?

Well, fleas are extremely common all over the world, and they can take up residence on pretty much any creature with fur.

That means fleas can find their way to your kitty from the groomer, the vet, an encounter with a mouse, or even a stray flea that hitched a ride from the neighbor's dog on your shoe and into your home.  

If you find fleas on your kitty, your first thought is likely what do I need to buy to get rid of these things and how long does it take for flea medicine to work on cats? 

Well, the short answer is, it depends on the type of medication you use. We’re going to get into that today, so if/when the time comes, you’ll have the answers you need. 

Cat parents raising kittens should watch the education video 🎥 on how to kill fleas on kittens. Dr. Robert Sidorsky, DVM 👨‍⚕️ offers his expert advise on this topic.

As always, if you are looking for more cat care resources, you can either skip all the way down to the bottom to the more cat care guides, or visit the toe beans pet parents blog, which by the way is loaded with 📚 resources, and you can search by topic.

Happy reading, learning, and sharing 😊

What Are Cat Fleas?

Before we take a deep dive into treating fleas in cats, I think it’s important to learn a little about these pesky bugs. Cat fleas are small bugs that survive on animal, or even human blood. So, fleas aren’t just a concern for your fur baby, it’s a concern for the humans in your life too.

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If your cat has fleas, whether they got them on an adventure outside or they sprang up seemingly from nowhere on your indoor-only kitty, it's important to get them treated right away. 

Fleas can lead to a variety of other infections, including tapeworms, anemia. And if that wasn’t bad enough, they can even infect you with diseases. Not to mention the flea allergies, itchy bites, and skin irritation they cause with their feeding habits!

“Cat fleas have been implicated in the spread of plague and the bacterial disease murine typhus through rats. They can also transfer tapeworms, specifically the dog tapeworm, Dipylidium canninum (Linnaeus), and the rodent tapeworm, Hymenolepis diminuta (Rudolphi). These tapeworms occasionally infest humans, especially very young children. The dog tapeworm infests cats that spend time outdoors.” – Pestworld.org.

How do I know if my cat has fleas?

The most common signs of a flea infestation include:

  • Scratching
  • Unusual licking or biting at their skin (especially in warmer locations like the groin, ears, between the toes, and inside folds of skin)
  • Skin redness
  • Fur loss
  • Black dirt like substance in their coat
  • Appearance of salt and pepper residue on their bed

Fleas have different stages of life, so when it comes to treatment it’s important to choose an option that will kill all stages.

Life cycle of fleas
Source: CDC,gov

Anti-flea medications come in several forms, which work in different ways and at different speeds. So, how quickly will your furry friend see relief? The good news is, it's generally not very long.

The First Flea Medicine for Cats: Collars

Flea collars are typically used as a preventative measure, but they can also be used to treat an infestation. You might wonder how they even work, after all how could a simple collar deal with fleas throughout an entire animal's coat?

The answer is, chemically. A flea collar is basically a collar infused with medication.

That medication works its way into your fur baby's skin and body and is circulated throughout their system. It is then excreted again through skin oils, which appear all over their little fuzzy body – thus killing the fleas that have setup shop.

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Flea collars will start to take effect within 24 hours, and your pet will start to experience some relief the day after the collar is put on. That is, assuming they're calm enough to keep it on.

For cats that hate collars, a flea collar is not a very effective way of treating fleas. Since it's a slow-release chemical, it needs to stay in place for a while.

In fact, for the best effect, a flea collar should be used for at least 3-4 weeks before it takes full effect – hence the reason they are primarily used as a preventative measure.

Cat in a Flea Collar Image by Toe Beans

There are also different kinds of flea collars. Some may target adult fleas, while others target eggs and young.

The life cycle of a flea is about three months long, which is why flea infestations can reoccur so readily; you stop seeing fleas, you stop treating for them, and then boom: they come right back. It's not even a new infection; it's just eggs from the previous batch hatching anew.

If flea collars take weeks to fully work, why do people use them? Well, for pets that tolerate flea collars, it can be an effective, long-term way to control the infestations. They're also relatively budget-friendly compared to other medications.

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On the other hand, some flea collars can be a bit intense, and the medication can cause redness and irritation in extreme cases (and for sensitive kitties.)

The medication is also transferable, so it can get into your system if you spend much time in contact with your fur baby, which you obviously do. This can be particularly dangerous for pregnant women and for human babies.

While it might seem like you can just pop down to the pet store and pick up a flea collar, it's usually a good idea to talk to your vet first in case there are other, better options you can try before.

The Second Flea Medicine for Cats: Topical Ointments

Topical ointments are medications that come in the form of a cream or lotion-style goop. This medication may be designed to be applied once per month or on a different schedule.

For example, some variations on the medication are meant to be applied every three months instead.

Some of these medications are flea-specific, while others are general antiparasitics and can kill ticks and even worms. This all depends on the brand of medication and the style you get.

You should, of course, generally talk to your vet before picking a medication so you don't get something unnecessarily strong or that could cause side effects for your poor fur baby.

Applying a Topical Ointment Image by Toe Beans

Applying these medications is relatively simple. The main thing to know is where to put them. You want to put the medication on the back of the head and the scruff of the neck.

This is so your furry child can't lick it. They may still rub it against furniture or use a paw to work at it, but the main thing is making sure that the bulk of the medication stays where it is.

Topical medications will generally take effect within about 12 hours, and by the end of 48 hours, your fur baby will be mostly flea-free.

There may be a few stragglers, and you'll still probably want to give them a bath to wash away eggs and lingering critters, but the medication will do the bulk of the work.

These medications generally work by making your fur baby's skin a hostile environment. Fleas feed on blood, and to get at that blood, they need to bite into the skin of your pet.

Unfortunately for them, once a flea medication has spread throughout the body, it infuses the skin and makes it deadly for the flea to bite. Any new flea showing up is in for a rude time.

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I’d like to add a word of caution here, stick to brands recommended by your vet. The cheaper options available in big box stores can be tempting, but they may be less effective and more likely to cause skin irritation.

Case in point: Back in college, over summer break, my sister bought a topical flea medicine for her kitty. It came as a two pack, so she figured she’d just give the extra dose to one of my boys.

She applied it as directed and shortly thereafter my Moosie began scratching. He couldn’t reach the exact spot, but I could see he was uncomfortable. I separated his fur by his shoulder blades and his skin was bright red.

I immediately tried to remove the ointment that was applied, but it was too little too late. He remained itchy and a little spot of his skin scabbed over as it healed from the ointment.

The Third Flea Medicine for Cats: Oral Medications

Any oral medication can be a challenge to give a cat. While pill “guns” and “pockets” are readily available, some cats are going to make you work hard to get them to swallow a pill.

There are also those smart cats that will eat everything you hid a pill in but leave the pill behind. I also love when they hid it somewhere in their mouth and spit it out later!  Have you ever had that happen? I have.

Once you’re able to get the pill swallowed by your kitty, it can begin doing its job. The typical oral flea medication is stored in your cat's lipids, or fat.

When a flea bites your kitty, it drinks a bit of blood and also the medication. What happens next depends on the medication.

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Some medications cause an overstimulation of the flea's nervous system, which kills the adult flea. This kind of medication kills adult fleas but doesn't do anything to new fleas hatching until those fleas feed, though, so it's not usually the best solution. 

Remember the life cycle we talked about above? You don’t want the cycle to continue indefinitely by just killing the adults as they bite.

Another kind of oral medication doesn't do anything to adult fleas. What it does is essentially causes a birth defect in any eggs the flea lays so that the fleas that hatch cannot form an exoskeleton and, consequently, aren't capable of surviving.

Giving Cat Oral Medication Image by Toe Beans

Combined, the two medications are pretty effective at getting rid of a flea infestation, and they can last for up to a month in general before they need to be reapplied.

Obviously, talk to your vet about the right kind of medications; you don't want to combine two if it would hurt your fur baby, after all.

The real question, though, is how long they take to work. This is where it turns out to actually be pretty great; oral flea medications start working within 3-4 hours – some even claim to start working in 30 minutes!

It can still take a bit of time before all of the residual fleas are gone, but it's still generally quite effective.

The tricky part with oral medications, other than making sure your cat will even swallow them in the first place, is that they're internal medications.

They can cause side effects or problems more so than other flea treatments, and in cats with epilepsy, they can even be dangerous.

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Other Kinds of Flea Treatments

There are a few other kinds of flea treatments that may be in order, depending on the situation and the severity of the flea infestation.

For example, if you're rescuing a flea-ridden kitten and their infestation is extreme, something like a medicated flea bath might be the way to go.

Check out this educational video on how to kill fleas on kittens by Dr Robert Sidorsky, DVM:

Flea baths are pretty unpleasant for many felines, but they're a good way to get rid of fleas pretty much immediately. Many fleas will flee the sinking ship, though, so you need to be diligent with cleaning up and using further preventative medications.

Cat Taking a Flea Bath Image by Toe Beans

An internet search might tell you to do a dish soap bath. Using a mild, fragrance-free dish soap will cause the flea to essentially drown in the water and a good scrub will remove the larva and eggs and wash those away as well.

One concern with the dish soap option is that it can be drying to the skin. Cat’s have less oil on their skin, so washing it away can lead to further skin irritation. So, if your kitty already has sensitive skin, ask you vet for a recommendation for a flea dip.

Flea combs aren't medications; rather, they're just fine-toothed combs that allow you to scrape scrape fleas and their eggs physically out of your fur baby's coat. They can be a good way to remove fleas while you wait for a medication to take effect.

Another potential option is the "natural" flea medications. Pyrethrins are a natural set of chemicals that come from chrysanthemums and, when refined, become something like a neurotoxin to fleas.

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They're not toxic to your fur baby (in reasonable doses), but they're absolutely deadly to fleas. This is one of the oldest kinds of flea treatments, and for a good reason. They also tend to kill other kinds of parasites, like lice and mites.   

There are also variations on the topical model, such as sprays and wipes, which can apply a medication more broadly over your fur baby's coat.

These are often less effective and less long-term than topical or oral medications, but they can be effective for spot treatments and getting rid of some fleas while you wait for another medication to kick in.

Fleas Keep Coming Back: What to Do

One of the most common issues with fleas is that they just keep coming back. One single adult flea can lay dozens, if not hundreds, of eggs, and that means many more fleas once they hatch.

The first and best thing you can do is give your fur baby a flea treatment on a regular basis, according to the instructions on the medication you're using.

This may be once a month (for some topical and most oral medications) or once every three months. Flea collars can also be effective for ongoing treatments.

Ongoing flea treatments make sure that even if a flea gets in and finds its way to your fur baby, it won't stay there. Either it will die right away, or it won't be able to lay viable eggs or both.  

You should also make sure that any other pets in your home are treated appropriately, especially any that go outside, like dogs. We love all our fur babies equally, even if they stay inside or go on adventures, and they should all be protected, right?

Treating a Cat for Fleas Image by Toe Beans

Remember, even if your indoor cat never goes outside, they should still have flea prevention medication used because fleas don't respect your property lines.

Even people coming to visit can bring fleas with them! Moreover, your fur baby could pick up fleas at the vet or at the groomer, too.

You should also take steps to make sure that rodents don't find their way into your home, or if they do, they have no reason to linger.

Remove food scraps from counters and the floor, store pet food in airtight containers safe from rodent infestation, and seal up ways a rodent could get in.

You'll also want to make sure to keep your home clean, especially if there's been a known flea infestation.

Fleas and flea eggs can linger for a surprisingly long time in the household, hiding in carpets, in dust, and in out-of-the-way corners, just waiting for the next time your fur baby comes along.

If your kitty has had fleas, be sure to wash all of their snuggle items like beds and blankets. Don’t forget to vacuum the couch and any cat trees.

Have you had to fight off fleas on your fur babies? In the end, what options did you find that worked the best? Tell us your story in the comments; you know we love to hear all about them!

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One more thing, if you are feeling like getting a little special something for your fur baby that is unique, made right here in the USA, 100% pup and cat safe, USDA certified organic and brought to you by a US company, check out Toe Beans  online pet supplies store!

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K Marie Alto
K Marie Alto

K. Marie is an animal lover, wife, kitty mom, dog auntie, writer, and co-founder of Toe Beans, a proud American family-owned online boutique pet supplies store focused on the improvement of the life of furry family members via pet parent education, better products, and advocacy. She has over 20 years of experience as a pet momma. She loves sharing her personal journey and experience as a pet parent via her blog and Facebook page where she currently has more than 30K followers (@furrytoebeans) and counting :-).

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