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Comfortis Vs Capstar for Dogs and Cats

Comfortis Vs Capstar for Dogs and Cats


Which Instant Flea Pill Works Best?

When your pet has fleas, you want to kill them NOW but what’s the best product to do that with?

You want to provide them with relief, not nausea and side effects so we’re going to break it down for you and tell you exactly what the differences are between Comfortis and Capstar, two of the leading instant flea killing pills available.

What Do They Do?

Both Capstar and Comfortis are meant to be used as a jumpstart for your flea program. All fleas will be dead in as little as 4 hours and no later than 24 hours. Capstar does this using nitenpyram, a neurotoxin to fleas. It kills all adult fleas within 24 hours and is safe for use in puppies and kittens as young as 4 weeks old as long as they weigh at least 2 pounds. It’s only effective for 24 hours.

Comfortis uses another flea neurotoxin, spinosad. It starts killing fleas within 30 minutes and provides protection for a full 30 days. It’s safe to use in puppies and kittens 14 weeks of age and older that meet weight requirements: 3.3 pounds for dogs and 2 pounds for cats.

Side Effects and Warnings

Side effects are pretty much identical between Capstar and Comfortis. The most common side effect is vomiting and you can reduce the odds of this happening just by administering the pill with food. Other side effects include:

  • Hyperactivity
  • Lethargy
  • Increased appetite
  • Diarrhea
  • Drooling
  • Excess vocalization
  • Hives or red skin
It should be noted that spinosad has been shown to interact negatively with high doses of ivermectin, the active ingredient in many heartworm pills including HeartGuard, so just as a precaution, you should be extremely careful combining the meds.


There are two primary differences between these two chewable flea pills.

  1. Comfortis is effective for a full 30 days but isn’t safe to use on small or really young puppies or kittens.
  2. Capstar is safe to use on young, small animals but is only effective for 24 hours.

In other words, it will kill the fleas but you need to start a regular flea control regimen immediately.

Which pill is most suited to you is dependent upon whether you need a quick fix or a long-term solution. Typically, Capstar costs a bit less than Comfortis so it may be a solution for immediate relief if you’re treating your home as well and your pet doesn’t spend much time outside.

If you’ve used either Capstar or Comfortis, please tell us about your experience in the comments section below.

9 Responses to “Comfortis Vs Capstar for Dogs and Cats”
  1. Karen says:

    I bought capstar for my dog and was very impressed with it. My little pom is almost 14y/o and weighs 7 pounds and has very sensitive skin and he had no problems at all with it. It took about about 3 hours but then the fleas were dead. I also put frontline plus on him also for a longer lasting method.

    • Larry Germansky says:

      Once the fleas were dead did the product protect the dog from any other fleas that might be in the carpet?

  2. Debra says:

    I have been using Comfortis for around 7 years for my chihuahuas. One of them came with some kind of I dont know what to say other then skin condition that no one had ever seen before when he was a puppy so after trying s many other things he was as a last resort placed on Confortis and that worked when all others failed. While he was taking it I researched and read how so and so had a death of their pet and claimed it was Comfortis. I never had any issues, problems, nothing using it and I even got scared at one point and went to Frontline and Advantax and some “new” just out stuff but always came back to Comfortis. Thank God for it and I am a customer for life!

  3. jacque says:

    I have used comfortis and it was effective right away. However it broke my dog out and her skin was irritated and red. It looked like she had brown, age spots on her and she developed body odor. The vet said allergic to fleas. but, again it happened after giving her this pill. I had to give her AN ALLERGY
    pill to stop her itching. Next I will try Capstar.

  4. Lucia Mauloni says:

    bought comfortsis this morning…on the instruction it says starts to work in 30min 100% fleas dead in 4hrs….well they are still there running around. if not dead in the morning going back for capstar….using sentinel for long term

  5. Kevin says:

    Got comfortis, cleaned all the fleas from my home within a week, my cats within a day, and it lasted over a yr before needing another dose.

  6. Erin says:

    We gave our cat comfortis multiple times (topical liquid alone was not enough because of her allergy to flea bites). The first few times she had no problem, but the last time we gave it to her she had such a bad reaction that we thought she was going to die. She would’t eat, she was drooling, she wouldn’t move: we felt terrible because we had poisoned her. We never used the product again. She recovered in a couple of days.

  7. Danny says:

    We used Comfortis for our 88 pound dog. We were told that it would keep fleas away for 3 months more or less. After 5 months, she started scratching and we saw signs of fleas. Since the Vet did not have Comfortis for her weight the second time. We purchased Capstar, and unfortunately I must say with no effect whatsoever. Our dog is scratching a lot and she’s covered with fleas.

  8. susan says:

    Very impressed with Comfortis. This has been a terrible year for fleas. Tried every over the counter product including herbal solutions (which I prefer) over several months and nothing else worked. Within a few hours of his first dose my cat had relaxed enough to nap, and within 3 days his skin had healed enough so he wasn’t constantly itching.

    I’m so pleased with this option.

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