Is My Pet's Flea Medicine Still Working? How Long Do Flea and Tick Meds Last?

Jennifer Coates, DVM
By Jennifer Coates, DVM on Jan. 26, 2015

By Jennifer Coates, DVM

Would you like to reduce the number of flea and tick treatments you have to give to your pets? If so, you have probably found yourself wondering whether or not the flea and tick medication you gave at some point in the past is still protecting your pet.

The answer depends on what type of flea and tick medicine you use. Some products have almost no residual activity, meaning that even if they are effective at killing fleas and ticks that are already on your pet, they do almost nothing to prevent new parasites from reestablishing an infestation. In these cases, a missed dose can quickly lead to treatment failure.

The most popular flea and tick medications for dogs and cats last for at least a month; some are even effective for eight to twelve weeks! Information about exactly how long a particular product works against different types of parasites is readily available on the medication’s label, manufacturer’s website, or by talking to your veterinarian.

Protect Your Pet Year-Round

The Companion Animal Parasite Council recommends that dogs and cats receive year-round protection against fleas and ticks. The reasons behind this are simple. Even in areas with bitterly cold winters or extremely hot and dry summers, fleas can easily live out their entire life cycle inside a home. Changes in climate are also making it more difficult to predict exactly when flea and tick seasons start and stop. Incorrectly timed or missed doses of medication put dogs and cats at risk for having fleas and ticks and increase their vulnerability to the diseases – Rocky Mountain spotted fever, ehrlichiosis, Lyme disease, anemia, and more – that these parasites can carry.

Year-round treatment for fleas and ticks is best, so pick a product that is easy to give. Collars, spot-ons, pills, or chewable tablets are all reasonable options. Make your choice based on how frequently you want to give the medication and any other concerns that you might have. For example, cats are extremely sensitive to some types of flea and tick medications; even low level exposures can cause illness. For this reason, people who own both dogs and cats may chose to avoid applying topical medications that can be toxic to cats onto their dogs. Before giving any flea and tick treatment to a cat, always double check that the label says it is safe for use in cats.

Protect Your Home, Too!

Another important tool for eliminating parasite infestations is environmental control. Thoroughly vacuuming carpets, floors, and upholstery is the best way to physically remove flea eggs and larvae from the environment. Put pet bedding, linens, and anything else that can be washed through the hottest washer and dryer cycles possible. This is usually all that is needed as long as every pet in the house receives an effective flea and tick medication year-round. If you are dealing with an especially severe infestation, house and yard sprays can also be helpful.

Whatever type of flea and tick medication you chose for your pets, read and follow the directions on the label to maximize its effectiveness. If you have additional questions or concerns, talk to your veterinarian.

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Image: Sakonboon Sansri / via Shutterstock

Jennifer Coates, DVM


Jennifer Coates, DVM


Dr. Jennifer Coates is an accomplished veterinarian, writer, editor, and consultant with years of experience in the fields of veterinary...

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