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Are Comfortis and Trifexis killing dogs?: FDA records 340 dog deaths associated with these drugs.

By Dr. Andrew Jones


There are 2 new drugs in the veterinary market called Comfortis and Trifexis. The company manufacturing the drugs claims they are safe, but there have been over 26,000 dogs with reported side effects, and over 300 dog deaths.

What is it?

Trifexis and Comfortis are monthly chewable tablets for dogs. Trifexis kills fleas and prevents flea infestations, treats and controls hookworms, whipworms and roundworms, and prevents heartworm disease. Comfortis is used specifically for fleas.


Trifexis contains 2 drugs: (spinosad + milbemycin oxime). Milbemycin has been used for 20 years with virtually no side effects. Comfortis contains spinosad. The concern is with this ‘new’ drug, spinosad.

Here is what the company has to say about side effects with Trifexis (source: Elanco)

As with all medicines, sometimes side effects may occur. In some cases, dogs vomited after receiving Trifexis. If vomiting occurs within an hour of administration, re dose with another full dose. During field studies, no severe or prolonged vomiting occurred. Additional adverse reactions observed in the clinical studies were itching, decreased activity, diarrhea, inflammation of the skin, redness of the skin, decreased appetite and redness of the ear. All reactions were regarded as mild

The company makes similar claims about Comfortis.

The most common adverse reaction reported is vomiting. Other adverse reactions reported in decreasing order of frequency are: depression/lethargy, decreased appetite, incoordination, diarrhea, itching, trembling, excessive salivation and seizures.

FDA Adverse Drug Reports

The FDA compiles adverse drug reports, and there are a huge number reported on spinosad, the new drug in Comfortis and Trifexis. In going through the FDA reports, I counted over 400 different adverse drug experiences in dogs, and over 10,000 dog owners reporting side effects.

Here are over 40 of the adverse effects:



Clearly there are serious problems with this drug, and the FDA should be warning pet owners and veterinarians about these potential side effects before more dogs become ill or die.

In the interim I would suggest to not give your dog Trifexis, or dose your dog or cat with Comfortis.

Best Wishes,

Dr Andrew Jones, DVM

P.S. Please forward this to other dog owners you may know.

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Topics: Dog Health, Pet Care, Pet health | 56 Comments »

56 Responses to “Are Comfortis and Trifexis killing dogs?: FDA records 340 dog deaths associated with these drugs.”

  1. Kari rairdin Says:
    May 20th, 2016 at 2:41 am

    Check out Brewers yeast and apple cider vinegar ……. I’ve also heard amethyst crystals are effective (the fleas don’t like the frequency of the crystals) ……I researched natural flea and tick repellent and found a website that had the top rated natural methods. I just crush up an apple cider vinegar bill and give a full one to my lab and have a one to my chi-winni …..I truly believe all the weird things our animals are dying from is from all the weird things that we feed them….. We are what we eat!

  2. Elizabeth Gray Says:
    June 7th, 2016 at 7:47 am

    I so wish that I had read everything here a long time ago, and yes, thank you Dr. Jones for your study and your conclusion. I have also gone on Trifexis deaths sites/blogs and read one horror story after another. This weekend, my beautiful four year old 120 # German Shepherd and I were having the nicest normal normal normal Saturday morning. It was time to give him his monthly Trifexis dose with his breakfast. I called him to me, slid the pill down his throat, gave him a treat and chased it with his breakfast. I made a point of keeping him inside with me for at least an hour to make sure that he didn’t vomit it up (as he did on more than one occasion when he was a young pup.) A little later, I said to him, George, let’s take a nap. He lay right by my bed and when I awoke, George didn’t lift his head. I jumped down and touched him…though he was warm, he looked sedated. He’d stopped breathing, his tongue was hanging out, his eyes were wide open. Everyone is entitled to their opinions, but in my view, there are just too many coincidences of these instances when a perfectly healthy, normal dog is dosed and dies. Dose to death: 6 hours. I’m on a personal crusade to boycott Trifexis and Comfortis and get the warning out to other pet owners. I only wish that I’d done my research before this tragedy and heartbroken for everyone else that has suffered the consequences of these drugs. Shame on you Elanco.

  3. Kimberly Mcmillon Says:
    June 8th, 2016 at 4:48 pm

    My little maltipoo still suffers seizures because of trifexis. He started taking it when he was 1 year old. My vet prescribed trifexis. His first seizure at 18 months old. The vet stopped giving him the medicine. He is now 5 years old and still has them. I wondered if a law suit has been started because of the problems with so many dogs.

  4. Frances Says:
    July 28th, 2016 at 3:13 pm

    My cat died recently and I believe it was due to the use of Comfortis and Cheristin for Cats. It was a horrific death and she displayed many of the symptoms shown here including ataxia, fever, vomiting, abnormal behavior including running around in circles, etc. After 8 months of this the only dx I was able to get is that she had no sensation in her spine. In the end, she got so sick I had to have her put down as she was 1/2 her weight and vomiting blood and foam.

    No one seems to care. I am sicked by this incident. If anyone is trying to do something about these tragic pet deaths, please post here! Thank you in advance for any help at all!

  5. Kathleen Gliva Says:
    September 15th, 2016 at 2:43 am

    I have now lost two pets and will NEVER give my pets oral medication for fleas or ticks. These are dangerous drugs!!!

  6. Zac Klausman Says:
    October 22nd, 2016 at 6:47 pm

    Hello, EVERYONE DO NOT USE TRIFEXIS! It recently killed my 7 month old Cane Corso I have been studying up on this drug and in process of a class action lawsuit! Please if anyone has had a pet die and had a necropsy done please contact me on FB! Its essential to collect information!




Dr. Andrew Jones, DVM
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