How Long Does Flea and Tick Medicine Last?

Published May 28, 2024
A pet parent applies topical flea and tick prevention to their Corgi.

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Flea and tick prevention keeps cats and dogs protected from external parasites and the various diseases they can transmit.

These diseases range in severity from itchy skin to more serious conditions like blood infections. Fleas and ticks can even cause diseases in humans, which is another important reason to keep them off pets and out of the house.  

Flea and tick preventatives are available in topical and oral options to meet the needs of each individual cat or dog. Products may be given monthly, bimonthly, or trimonthly depending on the type chosen and the pet parent’s preference. Single-use collars are also an option for pets and are effective for up to eight months.

When choosing a flea and tick product, pet parents should carefully read the labels to understand the correct dosing and the parasites each product protects against. Additionally, knowing the expiration date on the label ensures pets are receiving timely medication that’s optimally effective.

If you have any questions or concerns, contact your vet before administering or applying any flea or tick product to your pet.

How Long Does Flea and Tick Medicine Last?

The length of time that flea and tick medications last depends on each product.

Let’s discuss the three most common options that are available for pet parents to choose from.

Oral Flea and Tick Prevention

Oral flea and tick medications are available for both cats and dogs, and depending on the product, they are given every month or every three months.

These medications are administered orally and absorbed into a pet’s bloodstream, and fleas and ticks die after they latch directly onto the pet. The medications contain chemicals that cause paralysis in fleas and ticks.

Many of these products begin killing fleas and ticks in just a few hours after administration. For example, Credelio™ works in as little as six hours and lasts for a month, while Bravecto® starts working after six hours and lasts for one to three months, depending on the product type.

Other oral flea and tick medications for cats and dogs include:

Topical Flea and Tick Prevention

Topical flea and tick products are another option that pet parents may choose for their pet’s flea and tick protection. These products are applied monthly or bimonthly, depending on the brand.

Topical products are applied directly to the skin between a cat or dog’s shoulder blades.

Pet parents should part the fur in this area and gently squeeze the applicator until the correct dose of medication has been applied. The medication should be applied close enough to the neck that the dog or cat can’t lick it off.

Some topical products are effective only after they are absorbed into the bloodstream, while others remain concentrated in the skin and hair follicles. Topical medications repel and kill fleas and ticks by interfering with the parasite’s nervous system.

The amount of time it takes for topical products to work varies based on brand, but one product —Bravecto PLUS® for cats—kills fleas in just 12 hours and ticks within 48 hours following administration.

Another cat product, Advantage™XD, kills fleas in four hours or less but is not effective against ticks. Topical products last one to two months depending on the brand used.

Topical products containing permethrin—which is found in K9 Advantix™ II—should not be used on cats because this ingredient is toxic to cats.  

Cats in the home should be separated from dogs receiving this preventative until the medication has dried (about 24 hours after application) to avoid accidental ingestion if the cat rubs up against or licks the treated dog. 

Other examples of topical flea and tick medications for cats and dogs include:

Flea and Tick Collar

Several flea and tick collars are available, but the one most commonly used is the Seresto® Flea & Tick Collar. These collars are used for both dogs and cats. Flea and tick collars protect pets for eight months if they remain on the animal continuously.

The collar works by slowly releasing two medications —imidacloprid and flumethrin—into the skin that disperse and effectively kill fleas and ticks on contact. It kills fleas within 24 hours and is effective against ticks within 48 hours after applying the collar to the dog or cat.

After eight months, the collar must be replaced to continue providing protection to your pet. It’s important to note that although the collar is water-resistant, it’s less effective for dogs who swim or are bathed more than once a month.

In these instances, the collar protects against fleas for five months and ticks for seven months, so pet parents will need to replace their pet’s collar more frequently.

Brittany Kleszynski, DVM


Brittany Kleszynski, DVM


Dr. Brittany Kleszynski is a veterinarian and freelance medical writer who specializes in creating meaningful content that engages readers...

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