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Trifexis Vs Comfortis: Comparing Effectiveness and Safety for Dogs

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.

14 Responses 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.

    • Kathy Runk, CVT says:

      So sorry for your loss. I don’t think you should blame Trifexis-you should have gone back to your vet. The standard “protocol” is NOT to give ANY heartworm preventative to a positive animal! This is in the literature that comes with these products and the information given to veterinarians. It sounds like you have a possible malpractice case. I know suing the vet will not bring back Bruno but it might prevent someone else losing their pet.

    • becky yeager smith says:

      I’m livid Dianne reading your story…No need to ask if it was your regular vet…bc it does NOT matter. They ALL do the most absurd things for money. Obviously VETS don’t recite an oath of “first do no harm”. My 12 yr old miniature dachshund had many health issues.I was certain Mike would not (AGAIN) bring her home this time. She was bleeding from every orifice in her body. Those money-grubbers put my Gretchen on a drip saying they would “see how she was doing in the morning!” I told them they better do the humane thing. Can you believe it!

  2. Jeffrey Lear says:

    I’ve got 3 dogs (indoor/outdoor) and 3 cats (indoor)… I have been having lots of problems with Trifexis NOT being effective on the dogs. All three are scratching all day and night. Now the fleas are on my indoor cats.

    Even before fleas got on the cats, I found Trifexis uneffective on the dogs. Sarah is 72 lbs, Chester is 46 lbs and Cysco is 22 lbs. Each have a different dosage, so I’m thinking they are marginal with their weight.

    I have to visit the Vet Clinic and question them I guess.

  3. pat butcher says:

    I have used both Comfortis & Trifexis,but my dog had problems with both products. I gave them after meals & with meals,but he still vomited a lot and I was afraid with the Trfexis that he wasnt getting enough of the heart worm medicine. I had to go back with Heart Guard & Advantage11. These do not make him sick,I think because I give them several days apart. I feel the pills are very convenient,but too strong for my dogs system.

  4. Cesar says:

    Dianne, i am sorry for your lost. Trifexis is a great medicine but at the same time very very expensive. Especially when you have five dogs like me. I have used comfortis in the past and it works great. You can instantly see a relief in the dogs after an hour or so. I have been debating whether to buy trifexis or not but its great because if you use comfortis or trifexis and give them a different medication like ivermetin it could actually kill your dog or make them very sick. So you have to choose carefully and just like any medicine you give to your dog you should research before giving it to them. The only medicine that you can give safely to a dog with heartworms is tri heart, but you cant give them comfortis or trifexis while youre giving them tri heart because its lethal. Dont always trust your vet, There are tons of vets out there, some who care and some who do it as a job. If something seems fishy to you, dont be at all ashamed to take your pet and their records to a different vet. it could possibly save your pets life.

  5. Lori russel says:

    Been giving my dog trifexis and tested positive for roundworms. I give it every month exactly to the date!

  6. TREYGDAD says:

    I have just started using Trifexis on one of my two shih tzus because she seems to have a flea allergy and the 24hr kill period for advantixII is too slow.

  7. Macy says:

    I have a 6 month old puppy that has recently been placed on Trifexis. His fleas do not seem to be subsiding and I am worried he’s going to be miserable if I don’t do something soon. I bathed him in Dawn last week and it got rid of the fleas for a day or two but they came back. I gave him the Trifexis today and after about 4 hours, it is still not working. Should I switch him to Comfortis next month? Or is his dosage not high enough? Help!

  8. Jason says:

    I gave my puppy 1/2 of a trifexis pill and it almost killed her. And I noticed a clear liquid oily to the touch coming out of several spots on her back. And it was very painful to the touch in those spots. It even blistered her back and lost all hair in those spots. With antibiotics and mess for the blistering. My blue nose bully puppy is ok and the hair is growing back. But now the vet wants me to give her COMFORTIS FOR THE FLEAS??? Should I try giving her an oral flea pill? I am afraid that she cannot handle oral flea pills. It’s like instead of the trifexis distributing threw out her body it focused on only one spot??? I love my dog and want the fleas gone but I can’t stand to see her go threw that again. Any suggestions????

    • Mark says:

      Jason it seems like your blue nose pup has Demodex which is common in pitbulls especially blue nose. its unlikely that trifexis was the cause of the hair loss and blisters. unless she was having seizures and was vomiting i don’t see why using comfortis would be a cause for concern. i’ve been using comfortis for my pitbull pup and he’s been just fine.

  9. Phyllis says:

    I have used trifexis on my 2 small u(13 lbs) mixed breed dogs for almost a year. I tried another product for 2 months and fleas came. I put them back on Trifexis and they have been flea free and healthy and happy for the past 4 months.

  10. Betty Dietz says:

    My chihuahua has been on comfortis but I am thinking about switching her to Trifexis because I want to protect her from heart worm. the Comfortis has worked great for her. I have to give her something to eat before I give it to her or she will vomit and throw up.

  11. Maryann D says:

    I really liked Comfortis, found it safe and wonderfully effective, no vomiting and no fleas. My dog is a healthy male Shih Tzu, 7 years old, 11 pounds. But, my dog never liked the taste, so after six months of increasing difficulty in getting him to accept it, I am giving up and looking for something else. Its great if you dog is not a picky eater.

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