Flea and Tick Prevention for Dogs: Chews, Spot-Ons and Collars Explained
How the kinds of flea and tick prevention for dogs differ - isoxazoline chews, spot-ons and collars - which ticks US labels cover, minimum puppy ages, the FDA seizure caution, the EPA review of collars, cats and permethrin, and why vets advise year-round control.
AI illustration Flea and tick prevention for dogs comes in three forms: prescription chews (the isoxazoline class), monthly spot-ons, and collars. The chews differ in which ticks their labels name, how young a puppy can start, how long a dose lasts and whether heartworm prevention is built in; spot-ons and collars are mostly sold without a prescription and carry their own cautions. The Companion Animal Parasite Council recommends year-round parasite control for dogs. Which product suits your dog - its age, its health history, the ticks where you live - is your vet’s decision.
This is a reading guide to what the product labels and the regulators say - not veterinary advice. Doses, prescriptions and anything about a specific animal are your vet’s call; if your pet is unwell, contact a vet before you buy anything.
The Three Kinds of Product
Chews (isoxazolines)
How they work: the active ingredient - afoxolaner, fluralaner, sarolaner or lotilaner - circulates in the dog’s bloodstream, and fleas and ticks die after they bite. Pros: no residue for children or other pets to touch; swimming and bathing do not affect them. Cons: prescription only in the US; the whole class carries an FDA caution about rare neurologic reactions; the parasite has to bite to die.
Some chews add other drugs - moxidectin for heartworm prevention, pyrantel for roundworms and hookworms, praziquantel for tapeworms - so one monthly dose covers more.
Spot-ons
How they work: applied to the skin between the shoulder blades, the product spreads through the skin oils. Pros: the common dog spot-ons are sold over the counter; some also repel mosquitoes and biting flies. Cons: an oily patch until it dries, harder to apply on a large or wriggly dog, and it must be kept away from the dog’s mouth and from other pets until dry.
Collars
How they work: a collar releases low doses of its active ingredients slowly over the skin and coat, for up to several months. Pros: one purchase covers most of a year. Cons: works only while it is on and fitted correctly; frequent swimming shortens its life; see the safety note on collars below.
What the Labels Cover
The table lists common US products by active ingredient, with the brand in brackets so you can match what your vet mentions. Coverage, ages and weights are from the current US labels linked here; check the label of the pack you are given.
| Active ingredients (brand) | Form | Ticks on the US label | Heartworm | From |
|---|---|---|---|---|
| Sarolaner + moxidectin + pyrantel (Simparica Trio) | Monthly chew, Rx | Lone star, Gulf Coast, American dog, black-legged, brown dog, Asian longhorned | Yes | 8 weeks, 2.8 lb |
| Fluralaner (Bravecto) | 12-week chew, Rx | Black-legged, American dog, brown dog, Asian longhorned for 12 weeks; lone star for 8 | No | 6 months, 4.4 lb |
| Afoxolaner (NexGard) | Monthly chew, Rx | Black-legged, American dog, lone star, Gulf Coast, brown dog, longhorned | No (PLUS version: yes) | 8 weeks, 4 lb |
| Lotilaner (Credelio) | Monthly small chew, Rx | Lone star, American dog, black-legged, brown dog, longhorned | No (Quattro version: yes) | 8 weeks, 4.4 lb |
| Fipronil + (S)-methoprene (Frontline Plus) | Monthly spot-on, OTC | Ticks, plus fleas, flea eggs and chewing lice | No | 8 weeks, 5 lb |
| Imidacloprid + permethrin + pyriproxyfen (K9 Advantix II) | Monthly spot-on, OTC; repels mosquitoes | Ticks, fleas, mosquitoes, chewing lice | No | 7 weeks, 4 lb |
| Imidacloprid + flumethrin (Seresto) | Collar, up to 8 months, OTC | Fleas and ticks | No | 7 weeks |
A few label details worth knowing:
- The 12-week chew and the lone star tick. Its lone star coverage lasts 8 weeks, not 12, so vets in lone star territory may shorten the interval. That is a dosing decision for your vet, not something to adjust yourself. A monthly version for puppies from 8 weeks and a 12-month injection given at the clinic (approved in 2025) also exist.
- The oldest chew. Afoxolaner was the first isoxazoline chew, approved in 2013, so it has the longest record of use in the class.
- Food. The lotilaner chew must be given with food or within 30 minutes after a meal.
- Lyme disease. The sarolaner combination is also labeled for preventing Lyme infection as a direct result of killing black-legged ticks. A tick has to be attached for a while before it passes on Lyme disease - more than 24 hours in most cases, according to the CDC - which is why products are tested on how fast they kill attached ticks.
Permethrin is toxic to cats. Spot-ons containing permethrin, such as K9 Advantix II, must never be used on cats, and the label says to keep cats away from a treated dog for 24 hours. In a home where that is not realistic, ask your vet for a different product.
Two Safety Notes
The isoxazoline caution. The FDA advises caution with every product in the class in dogs with a history of seizures, because of rare neurologic reactions. For such a dog, products outside the class - some collars and spot-ons - exist, and the choice is your vet’s.
Collars and the EPA. In 2021, reporters found a high number of adverse event reports filed with the EPA about the Seresto collar, including reports of seizures and deaths. The EPA reviewed the reports and in July 2023 kept the collar on the market with new conditions: added label warnings, more detailed incident reporting by the maker, and a registration that runs for five years so the agency can keep evaluating reports. The regulator did not find grounds to pull the collar, and it did not close the question either. Discuss it with your vet, particularly if your dog has a history of skin reactions or seizures, and take a collar off and call the vet if your dog seems unwell after you put it on.
Questions to Bring to Your Vet
- Which ticks are here? Your vet knows which ticks and tick-borne diseases are common locally, and that decides which label coverage matters.
- Is heartworm prevention needed, and in the same product? A combination chew puts both on one date; a separate heartworm preventive works too. See our guide to heartworm prevention.
- How old and how heavy is the puppy? Every product has its own minimum age and weight.
- Does my dog have a seizure history? That steers the choice away from the isoxazoline class.
- Will my dog take a chew? If not, a spot-on or a collar.
- Does my dog swim often? Water does not affect chews; it shortens the life of collars and spot-ons.
- Is there a cat at home? That rules out permethrin products.
What About “Natural” Flea Prevention?
Natural products (essential oils, garlic, diatomaceous earth, apple cider vinegar) have no good evidence of effectiveness against flea or tick infestations. Vacuuming and washing bedding do reduce flea numbers mechanically, and diatomaceous earth can dry out live fleas on contact, but none of these provides reliable prevention or kills ticks fast enough to stop disease transmission.
Some essential oils are toxic to cats (tea tree oil among them) and can harm dogs in concentrated form, and garlic is toxic to dogs. Whether an indoor, low-exposure dog can get by with less is a question for your vet, not for a blog.
Year-Round vs Seasonal Prevention
The Companion Animal Parasite Council recommends year-round parasite control for all dogs, even in cold climates. Reasons:
- Fleas survive indoors - your house is warm regardless of winter outside
- Ticks do not disappear in winter - adult black-legged ticks stay active on winter days above freezing
- Mosquitoes that carry heartworm can linger in basements, sheds and other sheltered places
- Gaps are when infestations start - once fleas establish indoors, clearing them takes far more work and money than preventing them
Frequently Asked Questions
Can I get prescription flea and tick products without seeing my vet?
You need a valid vet-client-patient relationship for a prescription. Most vets will authorize an online pharmacy fill after an annual exam. In some states an online vet service can prescribe after a video visit; the rules differ by state.
Are flea and tick medications safe for puppies?
Each product has a minimum age and weight on its label - from 7 or 8 weeks for most monthly products, 6 months for the 12-week chew (see the table above). Always confirm with your vet for your specific puppy.
My dog had a seizure after a flea chew. What now?
Stop the medication and call your vet. The FDA has issued a safety alert about rare neurologic adverse events in the isoxazoline class. For dogs with a seizure history there are products outside that class; which one fits is your vet’s call.
Can I use the same product for my cat?
No, unless the label says so. Cats must not be given products containing permethrin, and the dog chews are not approved for cats. Cats need a cat product prescribed or recommended for them, such as a monthly cat spot-on that covers fleas, ticks, ear mites, worms and heartworm.
How do I check my dog for ticks?
Run your fingers slowly through the coat against the grain. Check especially: ears, behind ears, under the collar, armpits, groin, between the toes, tail base. Use a tick key or fine-tipped tweezers to remove a tick - grasp close to the skin and pull straight out without twisting. Save the tick in a sealed bag in case your vet wants to identify it.
What if a tick is already attached?
Remove it right away. The risk of disease grows the longer a tick stays attached. Dogs do not get the bullseye rash people do; over the following weeks and months watch for lameness, swollen joints, fever, lethargy or loss of appetite, and call your vet if any appear.
Why is my dog still getting fleas with prevention?
Three possibilities:
- A gap - a missed or late dose
- A product problem - the collar fell off, the spot-on was washed off too soon
- A source of re-infestation - fleas in the carpet, bedding or yard
Wash all bedding hot, vacuum often, and keep the dosing on schedule. Reports of products “not working” usually turn out to be gaps or re-infestation; if the problem persists, ask your vet whether to treat the home or switch products.
Summing Up
Prevention comes as a prescription chew, a spot-on or a collar. The labels differ in the ticks they cover, the youngest age they allow, how long a dose lasts and whether heartworm is included. Bring your vet the questions above - local ticks, heartworm, age and weight, seizure history, cats at home - and keep the dosing year-round, because a skipped month is how infestations and tick-borne diseases start.
Related Reading
Last updated: October 2026. Coverage, ages and weights are taken from the current US product labels; check the label of the pack you are given. The chews named here require a veterinary prescription.
