How Long Do Flea and Tick Medications Take to Work on Dogs?

Stephanie Howe, DVM
By Stephanie Howe, DVM on May 25, 2022

If you’ve found fleas or ticks on your dog, don’t panic. With the right treatment, these common pests can be quickly eradicated—often in a few hours. Fortunately, all flea preventions, both topical and oral, show great speed in controlling flea infestations. Topical preventions have been shown to clear current flea burdens on dogs within 12–48 hours, and oral preventions often work within the first two to four hours.

When it comes to ticks, both oral and topical options should cause tick death in 24–48 hours. Ask your vet about the best tick treatment for pets in your area, since not all treatments target the same kind of ticks. Ticks may need to be removed from your pet, as they may or may not fall off after they die. Routine checks of your pet’s skin to monitor for ticks are recommended, especially in areas that are highly populated for parasites.

Signs Flea and Tick Medication Is Working on Your Dog

After administering flea and tick medication to your dog, expect to see at least some dead fleas within 24 hours of treatment. However, it will probably take a few days for the itching to decrease. If your pet has a severe infestation, several rounds of treatment over several months will be needed to eliminate the problem, because the life cycle of the flea (from egg to adult) is about three months. 

Ticks are hardier than fleas, so it will take longer (closer to 24–48 hours depending on the type of treatment utilized) for a treatment to work. Dead ticks may or may not fall off your dog. It is generally recommended to have dead ticks removed by a veterinarian as soon as possible, to ensure that the head of the tick, which can be buried under your dog’s skin, is completely removed.

If you’ve been using a particular preventative tick medication for the first time and are seeing the same or increased numbers of ticks on your dog, tell your veterinarian. You might need another type of tick repellent.

How to Get Rid of Fleas and Ticks in Your Home

To get rid of all fleas and ticks, you must do more than just administer medication to your dog. It’s important to also:

  • Ensure that all pets in the home are on flea and/or tick prevention. This includes dogs, cats, ferrets, and rabbits.

  • Vacuum daily to remove flea eggs and larvae, even if you have hardwood or tile flooring. Make sure to discard the vacuum bag or empty the canister immediately after use.

  • Wash all bedding with hot water weekly.

  • Bathe your dog weekly to remove dead fleas if you’re managing a flea infestation.

  • Keep a neat yard. Fleas and especially ticks love shaded, dense areas, so keep a distance between your home and any forested areas, dense brush, or tall grasses.

  • Consider having a professional company come to spray your home and yard; just be sure it is a pet-friendly treatment.

  • Ask your vet about insecticides for home use. Sprays, bug bombs, or powders can be beneficial, but it’s crucial to only use pet-safe products and follow the instructions carefully. 

Treating Additional Problems Related to Fleas and Ticks

Fleas and ticks can cause itching, skin irritation, and inflammation just by their presence on the body. The greater the number of these pests, the more irritation. Many dogs are allergic to flea spit, which can cause a skin condition called flea allergy dermatitis,  where a dog may develop inflammation, itching, open sores, scabs, and hair loss secondary to the allergic reaction to the flea bite. The loss of fur and skin irritation most commonly appears around the lower back, tail, or hind legs.

Treatment depends on the severity of the dermatitis and may include use of medicated shampoos, medicated wipes, oral antibiotics, or anti-inflammatories.

In large enough numbers, fleas and ticks can cause anemia in dogs as they ingest a blood meal from our pets. If that happens, your pet may have pale gums or be lethargic. Treatment may be as simple as giving your pet an oral iron supplement, or if the anemia is serious enough, it may require that your pet get a blood transfusion.

Additional Diseases from Fleas and Ticks

While fleas and ticks can do a vast amount of damage to pets by themselves, they also can carry other diseases that can sicken your dog. Fleas are very likely to carry tapeworms, an intestinal parasite, and  several types of bacterial diseases such as cat scratch fever. If your dog has fleas and develops any additional symptoms like diarrhea, vomiting, or lethargy, talk to your veterinarian. They may recommend additional testing for one or more of these conditions.

Ticks often carry bacteria that may cause diseases including Lyme disease and Rocky Mountain Spotted Fever. Ask your vet if your dog should be tested for common tick-borne illnesses. If your pet has contracted a tick- borne disease, additional treatments such as antibiotics will likely be needed.

How to Prevent Flea and Ticks Year-Round

Year-round flea and tick prevention is paramount to keeping your dog healthy. There are many forms of flea and tick preventions, and it is important to work with your veterinarian to determine which is best for your pet.

Oral Flea and Tick Preventative Medication

While topical preventions have typically been the most common, new oral preventions are proving their worth with their rapid efficiency and ease of use. These are great products to utilize when there are multiple-species pet households or young children present in the home. Oral preventions are currently the most recommended product types by veterinarians.

  • Isooxazoline: Isooxazoline medications are a newer and highly effective preventative that offer great efficacy against fleas and several types of ticks. These medications include:

  • Spinosad: Spinosad is an effective oral flea preventative. This medication includes:

Comfortis and Trifexis do not prevent or treat ticks.

  • Nitenpyram: This is the only category in the oral preventative section that is over the counter. This product has rapid onset against fleas, but is only effective for 24 hours. These medications include:

  • Milbemycin/lufenuron: Milbenmycin is a heartworm prevention and lufenuron is a flea prevention. Lufenuron does not kill fleas. Sentinel is the only product on the market that contains lufenuron.

Topical Flea & Tick Preventative Medication

Topical preventions are liquid products that are generally applied to the skin at the nape of the neck. These products can be toxic when ingested (especially if a cat ingests a dog flea prevention), so it is important that these products have dried on dogs before other pets or children are allowed to interact with them. Bathing may affect the efficacy of these products; please see the product packing for more information.

The most common topical flea and tick preventative medications include:

Flea & Tick Preventative Medication Collar

These products are not all equally effective. Generally, older products use insect growth regulator ingredients (like tetrachlorvinphos or deltamethethrine) which have variable and questionable efficacy. These products should not be handled by young children. Seresto® is a newer product and has much greater efficacy than older products. It is labeled for over-the-counter use in dogs, works within hours, and can be effective for up to 8 months.

After handling any flea/tick prevention collars, pet parents should wash their hands thoroughly.


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Featured Image: Anikin


Stephanie Howe, DVM


Stephanie Howe, DVM


Dr. Stephanie Howe graduated from the University of Florida College of Veterinary Medicine in 2011, after receiving a Bachelor of Science...

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