Trifexis Vs Comfortis

Which Flea Tab is Right for You


Trying to decide which flea control product to use is difficult, especially with so many different options on the table.

Today we’re going to take a look at two of the top chewable flea control pills, Trifexis and Comfortis, and explain the difference between the two so that you’ll know which one is right for you.

We’ll start with what they can do, then move on to safety issues.

What Do They Do?

Comfortis and Trifexis share one common ingredient, Spinosad. This is an ingredient used in several of the leading flea treatments and kills fleas within 4 hours of administration. Unlike other oral flea meds, Spinosad continues to kill fleas for up to 30 days.

Also unlike many other flea killers, Spinosad only kills adult fleas; it doesn’t kill eggs or larvae and it doesn’t repel them.

Spinosad is the only ingredient in Comfortis so adult fleas are all that it is effective against. That’s fine, if that’s all that you need. Trifexis, on the other hand, has milbemycin oxime in addition to Spinosad.

Milbemycin oxime is a common ingredient used to prevent heartworms and intestinal parasites such as adult roundworms, adult whipworms and hookworms. It prevents heartworms by killing the juvenile worms in the bloodstream before they reach the heart.

Safety Comparison

Comfortis is safe to use on cats, kittens, dogs and puppies 14 weeks of age and older. Dogs have to be at least 3.3 pounds and cats need to be at least 2 pounds.

Side effects of Spinosad (the one in both Comfortis and Trifexis) are rare and include vomiting, hyperactivity, lethargy, increased appetite, diarrhea, drooling, excess vocalization, hives, and skin irritation.

Side effects of milbemycin oxime, the ingredient used for heartworms and intestinal parasites, include depression, drowsiness, nausea, skin irritation, drooling, diarrhea, loss of appetite and seizures. These are extremely rare as long as your dog doesn’t have heartworms when you give him the pill.


The bottom line is that both Comfortis and Trifexis contain Spinosad to kill the fleas that are on your dog, and keep them dead for 30 days. The determining factor for you is going to be whether you want to also treat for heartworms and intestinal worms. If so, then you’ll want to use Trifexis. Both pills are available only from your vet, so talk to him about it if you have more questions.

If you’ve tried Comfortis or Trifexis, or even better, both, let us know about your experience in the comments section below.

One Response to “Trifexis Vs Comfortis”
  1. Dianne says:

    I went to the vet I had been using and ask for Comfortis since this was what a friend had recommended for fleas. The vet gave me Trifexis. I didn’t realize at the time that there was a difference. My dog was tested for heartworms prior to them giving me the Trifexis and he tested positive. The vet told me to go ahead and start Bruno on the pills. It was the protocol even when the dog tested positive. I didn’t know any better. I came home on that Friday afternoon at 2:00 and gave him the pill, by 11:00 that night my beloved Bruno was dead.

    Trifexis is extremely powerful and used under the correct circumstances is probably very good. Don’t ever let any vet tell you that it is ok to use this particular flea and heartworm preventative on a dog that already has heartworms. IT WILL KILL THEM!!!! AND IT IS ONE OF THE MOST HORRIBLE DEATHS YOU CAN IMAGINE.

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