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Can I use 5lb cat flea medicine on my 7lb cat safely and effectively?

Updated On September 23rd, 2025

Pet's info: Cat | Mixed Breed | Male | neutered | 1 year and 6 months old | 7 lbs

Hi there! I have two cats, one is about five pounds and my othet older one is 7 pounds. I was wondering if it was safe, and if it could be effective, to use a topical flea medication for my 7 pound cat that states in the box is meant for a 5 pound or less cat? I was assuming that since it is a less dosage it would be safe and maybe still effective. But I’m still not sure and don’t want to just assume. The brand is “Sentry Purrscriptions Plus.” Thanks!

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2 Answers

Most Helpful Answer

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Answered By Lindsey Edwards MVB, BSc, IVCA

Veterinarian

Published on April 20th, 2018

It is likely to be safe but poorly effective as it would not have enough active ingredients for the size of cat. This would mean you would be undertreating and encouraging drug resistance in fleas (but not reducing the risk of any side effects should they occur). I strongly recommend using the correct size and strength for each cat

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    Answered By Menolly Cote, DVM, CVA

    Veterinarian, Certified Veterinary Acupuncturist

    Published on

    What cute kitties you have! While it would be safe to use a dose for a 5lb or less cat on your larger cat, it is likely that it will not be as effective as the appropriate dose would be. Given how difficult it can be to deal with fleas once you have them in the house, I would recommend using a high quality product in appropriate size. I prefer a seresto collar (https://www.petco.com/shop/en/petcostore/product/cat/cat-flea-and-tick/cat-flea-and-tick-collars/seresto-flea-and-tick-collar-for-cats or Bravecto for good flea and tick control. Seresto collars are available over the counter while Bravecto requires a prescription.

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