HomeResource CenterHow Does Flea Medicine Work

When and How Does Flea Medicine Work on Dogs and Cats

Medically Reviewed by

Tracy Isenberg, LVT

As a pet parent, you’ve probably heard about the dangers of fleas and ticks. So, how does flea medicine work, and what should pet parents know?

In this article, we’ll cover the ins and outs of flea medicine and answer important questions about how it can protect your pets.

Plus, we’ll touch on topics like:

  • Types of flea and tick medication
  • How topical flea medicine works
  • How long it takes to work
  • How often you should treat your pets
  • How to get the most out of flea and tick medication

Types of flea and tick medications

Types of flea and tick medications

There are plenty of medications out there that kill fleas on pets. But, not all flea treatments are created equally. Here are some common forms of flea treatments, and the benefits of each.

Topical medications

are the most effective medicine for killing fleas and preventing future flea infestations. Topical medications are different for dogs and .

Only give your dog flea and tick medication made for dogs. And, only give your cat flea and tick medication made for cats.

Here are some popular topical medications for dogs and cats:

Oral medications

Flea pills typically target flea eggs or adult fleas — but not both. Pay attention to what your oral flea medications cover.

Most oral flea medications do not prevent or kill ticks. So, find a treatment that also covers ticks for complete protection.

Here are some popular oral medicines for dogs and cats:

  • Dogs: Comfortis Flea Preventative
  • Cats: Credilo Chewable Tablets for Cats
Can you combine topical and oral flea treatments?

It is not recommended to combine different flea treatments to treat your pet for fleas and ticks. Exceeding the recommended dosage for flea meds can harm your pet.

Flea and tick collars

Preventive flea and tick collars can last up to eight months. The collar sits around your pet's neck and protects your pet from flea and tick bites around their shoulder blades, face, and neck area.

While flea collars can kill and prevent fleas and ticks, they are not as effective as spot-on treatments. Flea collars do not cover other parts of your pet’s body as well as spot-on treatments.

There are different collars for different weight breaks, so be sure you get the right collar for your pet's unique size.

Here are some popular flea and tick collars for dogs and cats:

  • Dogs: Seresto Flea & Tick Collar for Dogs
  • Cats: Seresto Flea & Tick Collar for Cats

Shampoos and powders

Shampoos and powders are non-medicinal options for pet parents. But, they are not long-term solutions for continuous flea control. Flea powders last up to one week, while flea shampoos only kill adult fleas already biting your pet. And, flea shampoos only last for about a day.

Here are some popular flea shampoos and powders for dogs and cats:

  • Dogs: Vet's Best Advanced Strength Flea & Tick Dog Shampoo
  • Cats: Zodiac Flea & Tick Powder for Dogs, Puppies, Cats & Kittens

How does topical flea medicine work

How does topical flea medicine work

Flea and tick medication works to kill adult fleas, flea eggs, and flea larvae on dogs and cats. Preventative medications protect your pet from flea and tick bites, skin irritation, and Lyme disease. And, they protect your pet from other diseases they carry.

Flea medicine works by overstimulating a flea's nervous system, which kills them. Flea and tick treatments work the same way but also work to kill ticks. Flea medicine also stops the development of flea larvae.

The best flea prevention for your pet has the right active ingredients, is applied correctly, and used consistently.

Find products with the right active ingredients

Your pet's flea and tick prevention should have active chemical ingredients that are safe for your pet's breed and weight. Plus, the active ingredients should kill and repel fleas effectively.

Some flea medications can have side effects. And not just any flea medicine is right for your pet. Talk to your veterinarian about which active ingredients are right for your pet.

Apply it correctly

Follow the instructions provided by your vet and the label on your pet's treatment when applying. Every treatment is different. So, follow each step carefully to ensure your pet is getting the best care.

Use it consistently

To effectively kill fleas and ticks (and keep them away), use flea medicine routinely. Some treatments last 30 days, while others can last for months.

Pay attention to when your pet's treatment will run out. Apply your pet’s treatment at the same time every month for the best results.


How long does flea medicine take to work

How long does flea medicine take to work

If your pet has fleas, treat them right away. Flea treatments work quickly and effectively to stop the flea life cycle and prevent further infestation.

Every flea treatment is different, but topical treatments and collars typically start killing adult fleas within 12 hours of application. Oral medications often work to kill fleas in two to four hours.

If your pet has a severe flea infestation, it may take several rounds of treatment to get rid of them. The life cycle of fleas (from egg to adult) takes about three months. And, these parasites can wreak havoc on your pets and your home.


How often to treat your pets

How often to treat your pets

The best way to remove fleas and ticks for good is through consistent protection. Pet owners should give their pets monthly flea and tick treatments on the same cadence as their pet’s treatment. This may be every 30 days or every 8 months. And, pet owners should use flea and tick prevention all year long.


How to get the most out of your topical medications

How to get the most out of your topical medications

Now that you know the ins and outs of flea medicine, here are the best practices for getting the most out of your flea and tick topical medications.

Follow the instructions on the label carefully.

Most topical treatments are generally applied to your pet's skin starting at the base of their neck. But, follow the instructions provided on your pet's treatment box.

If your pet has an adverse reaction to their flea and tick medication, visit your veterinarian immediately for a check-up.

Keep your pet dry for 48 hours.

Your pet's skin should be dry for at least 48 hours before and after application. This ensures your pet’s skin oils and hair follicles spread the treatment to work properly.

While applying spot-on flea and tick treatments, avoid bathing your pet with Dawn dish soap, or other soaps that strip the oils from your cat or dog's skin. Using these soaps may lessen the effectiveness of your pet's topical drops.

Stay on a routine schedule.

Flea season is every season. Fleas and ticks can survive indoors, even in the colder months. That's why pet owners need to treat their pets with flea and tick medication year-round.

Remembering your pet's treatment day doesn't have to be tricky. Choose a topical treatment with perfectly timed delivery, so your pet always gets their treatment on time.

Protect your home.

If you have a flea infestation in your home, use ahousehold spray. Best-in-class sprays cover a combination of fleas, ticks, and other pests.

Pair with heartworm prevention.

Fleas and ticks aren't the only parasites pet owners should worry about. Heartworms, hookworms, and roundworms can carry diseases and cause health problems in cats and dogs.

Heartworm disease is a serious health problem in dogs and can lead to death if untreated. Heartworm prevention works to stop the development of heartworms in your dog's body.


Cover all the bases of parasite control by treating your pet for fleas, ticks, and heartworms every month. Unsure where to start? Talk to your veterinarian about which treatments are right for your pet.

Dealing with cat fleas? Check out this helpful guide for getting rid of fleas on cats.