PetMeds® Comfortis Flea Control: Potential Side Effects

Did you know that not all flea control products for dogs are applied to the skin? Many pet owners prefer oral administration of external parasiticides to avoid exposure of themselves to topical pesticides, which is why some dog owners prefer the ease of administering a chewable tablet such as Comfortis. Comfortis can control fleas up to one month on dogs, but it does not kill ticks

Comfortis kills fleas within 30 minutes and lasts for up to one month. In my experience common client concerns include lack of efficacy against other external parasites such as ticks, as well as the need for written prescription from the veterinarian.

One of my concerns with Comfortis is the occasional wide range of side effects including vomiting and/or diarrhea and various neurological reactions ranging from incoordination, trembling, and seizures.  It’s for these reasons that I generally prefer using other flea and tick products in my practice such as Frontline Plus or Advantage II.

However, clients do report mostly high satisfaction with this product, with the exception of these occasionally severe side effects.  It is also important to still treat the environment for fleas, as well as incorporate additional measure to help control other parasites such as ticks if using Comfortis.

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  1. Our Shih-tzu had a reaction to topical flea meds, so vet prescribed a prescription flea spray that we used for 5 years. Then we moved to a hot climate and she got hook worms, so the vet put her on Comfortis. 6 months later at her regular 6 month check up, she now has liver disease! I dont think this is a coincidence. Nothing else has changed… we will be going back to the spray and now have to feed her special food and vitamins. :(

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