About Advantage II
Advantage II is a topical, over-the-counter flea treatment now owned and marketed by Elanco Animal Health, which acquired the Bayer Animal Health portfolio (Advantage II's original developer) in a $6.89 billion deal that closed in August 2020. The formula combines two active ingredients, imidacloprid and pyriproxyfen, and is sold in weight-banded doses for kittens (2-5 lbs), small cats (5-9 lbs), and large cats (9 lbs and up), all labeled for use on cats and kittens 8 weeks of age and older.
Imidacloprid attacks a flea's nervous system to kill adult fleas on contact, while pyriproxyfen is an insect growth regulator that stops flea eggs and larvae from developing, so the product works on both the flea on the cat and the flea life cycle in the home. Elanco states the formula kills existing fleas within 12 hours and continues protecting against reinfestation for 30 days. It is EPA-registered as a pesticide product and sold without a prescription; Elanco's own site markets it as a vet-recommended option and sells it alongside the company's other flea and parasite lines, including K9 Advantix II and the prescription-only Advantage Multi.
Brand website: yourpetandyou.elanco.com/us/our-products/advantage-ii
What Advantage II makes
Advantage II's range runs wider than the products we review. The lines we know best from our own testing are marked with a star:
Advantage II for Cats (Kitten, Small Cat, Large Cat)
Weight-banded topical spot-on doses for cats and kittens 8 weeks and older, 2 lbs and up — featured on House of Mittens
Advantage II for Dogs
Same imidacloprid and pyriproxyfen formula, weight-banded for puppies and dogs 7 weeks and older
K9 Advantix II
Elanco's flea, tick, and mosquito topical for dogs, a separate formulation from Advantage II
Advantage Multi for Cats
Prescription monthly topical adding heartworm, ear mite, and intestinal worm coverage to flea treatment
Advantage Multi for Dogs
Prescription monthly topical covering fleas, heartworm, sarcoptic mange, and intestinal worms
Why we recognized Advantage II
The House of Mittens Top Brand recognition isn't paid for and can't be applied for. We award it to the brands whose products consistently stand out in our vet-reviewed category guides. Advantage II earned it on the strength of the products below, evaluated the same way every product on this site is: assessed against feline-health criteria, used with real cats, and judged on merit.
Advantage II products we rated highly
Advantage II Large Cat Vet-Recommended Flea Treatment (Cats Over 9 lbs, 4-Month Supply)
In our testing, this was the fastest-acting monthly spot-on in the roundup, with a 4.5-star average across roughly 15,000 ratings and one of the steadiest track records in the category. It kills fleas within 12 hours and destroys eggs and larvae as well as adults, and its fragrance-free, no-prescription formula makes it a strong fit for a strictly indoor large cat that needs flea control without paying for tick coverage it won't use.
Read the 10 Best Flea Treatments for Cats of 2026 guide →
Advantage II Kitten Vet-Recommended Flea Treatment (Cats 2-5 lbs, 2-Month Supply)
Purpose-dosed for the 2-to-5-pound kitten weight band rather than a fraction of an adult tube, which removes the dosing guesswork on a small kitten. It uses the same imidacloprid and pyriproxyfen formula as the adult version, kills fleas within 12 hours, and needs no prescription, making it one of our top picks for young kittens 8 weeks and older.
Read the 10 Best Flea Treatments for Cats of 2026 guide →
Advantage II Small Cat Vet-Recommended Flea Treatment & Prevention (Cats 5-9 lbs, 1-Month Supply)
The insect growth regulator in this formula kills flea eggs and larvae alongside adults, which is the mechanism that actually breaks the household flea life cycle. It's one of the most widely used and most-reviewed cat flea products in the United States, available over the counter and priced to sustain year-round use, which is exactly what consistent flea control requires.
Read the Best Oral Flea Treatments for Cats of 2026 guide →What earned Advantage II the recognition
- A top pick across two of our cat flea treatment guides, spanning kitten, small cat, and large cat weight bands.
- Kills existing fleas within 12 hours in Elanco's own testing, and its pyriproxyfen component kills flea eggs and larvae as well as adults, addressing the full flea life cycle rather than just the fleas visible on the cat.
- Weight-banded formulations (2-5 lbs, 5-9 lbs, 9+ lbs) mean owners are dosing to a purpose-built product rather than estimating a fraction of a larger dose.
- EPA-registered, fragrance-free, and available without a prescription, backed by a deep base of tens of thousands of owner ratings across its cat product line.
- Manufactured by Elanco Animal Health, a company with a multi-decade legacy in the category through its 2020 acquisition of Bayer Animal Health's parasiticide portfolio.