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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 | 17 Comments »

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

  1. Kim Says:
    November 15th, 2013 at 1:20 pm

    Where is the link for FDA’s adverse reports regarding Trifexis? I searched everywhere and couldn’t find your referenced document regarding adverse affected in Spinosad. Could you please share the exact sources and references for this information? Thank you.

  2. Gloria Scott Says:
    November 16th, 2013 at 9:38 am

    My dogs have taken Trifexis for quite some time now…I have noticed itching but that is all.

  3. Tony knighten Says:
    November 16th, 2013 at 3:36 pm

    What would be a good substitute for Trifexis?

  4. teresa bilton Says:
    November 17th, 2013 at 8:18 am

    we have used Trifexis for a year now an love it no prob. an never a flea. also use the collar preventic an never get a tick before using we would pull off 1 or 2 a day

  5. Jason Says:
    November 17th, 2013 at 10:25 am

    I would use Heartgard and a topical for flea/tick

  6. Active vet Says:
    November 24th, 2013 at 7:14 am

    All drugs have side effects and yes ANY can cause death including basic vaccines. But the risk of not useing these life saveing products are much higher. This is a wonderful product that protects a lot of pets from Heartwrom disease, intestinal parasites and other zoonotic disease spread by flea bites. I am truly sorry for anyone that has lost a pet due to medication reactions but talk to a reputable qualified veterinarian about your concerns!

  7. R.D. Minter Says:
    November 24th, 2013 at 11:48 am

    After only 6 doses of Tirfexis one of my Schnauzers starting having GI Bleeding and on examination she had lost most of her Platelets and required 3 blood transfusions and three nights in the Emergency Pet Hospital. In addition, she had to be put on Steroids and almost didn’t survive. Within 30 days our second Schnauzer who was also on Trifexis started passing out and after examination by our Vet. she was diagnosed with inflammation around the Heart and Addison’s disease (lose of her Adrenal Glands). She progressively got worse and died within two weeks from multi-organ failure.

  8. Christina Says:
    November 25th, 2013 at 1:19 pm

    I agree w/ACTIVE VET: all medications come with a risk, even Tylenol for humans. Comfortis and Trifexis both SAVE thousands of pets each month by not allowing them to get too many fleas which may lead to anemia and other blood disorders or heartworm which is very costly to treat and even fatal.

    Talk to YOUR veterinarian, not one online.

  9. Paula Says:
    November 27th, 2013 at 12:32 pm

    PLEASE get your facts correct before blasting them on the internet. I want to see the FDA reports…if the FDA feels this drug is TRULY not safe, why has it not been pulled off the market??? The FDA isn’t making money on it! Oh, and why are you no longer a veterinarian???

  10. Iz Says:
    December 3rd, 2013 at 6:22 am

    The FDA isn’t making any money on pharmaceuticals? Think again Paula. FDA and big pharma are hinged at the hip and although we can file a complaint with them, it’s very unlikely they will respond UNTIL there is a very large number of associated deaths, illnesses or similar complaints- especially when they are being paid incentives by a drug company. Remember Vioxx and how many Americans died before it was banned? Tequin? My gosh, the Vioxx incident alone should have been a wakeup call to Americans to question their trust in the FDA. The truth is that most regulatory bodies in the US today are influenced by the industry they are supposed to be monitoring and regulating. At one time, the FDA really was trustworthy but not anymore dear. About 13 years ago or so, the FDA was beheaded and industry oversight became rather slack in an effort to further support deregulation of big corps including drug companies.

  11. Iz Says:
    December 3rd, 2013 at 6:46 am

    Instead of everyone just being complacent and accepting the fact that drugs have side effects, why not look for safer alternatives that are available? In some cases I have no choice but to use radical medicines and therapies but only when we are absolutely forced to. Alternative therapies in human and animal medicine are often dismissed as quackery, despite studies that demonstrate otherwise, for a multitude of reasons…mainly because the drug companies haven’t found a way to bottle and sell these therapies. FDA tried to shut down the cherry industry because cherries were proven to be more effective in the treatment of gout which competed with expensive pharmaceutical drugs. Why put yourself or your beloved pets at unnecessary risk? My first line of defense is nutrition for myself and my animals. I don’t believe in quick fixes even though they are certainly more convenient because according the first law of thermodynamics, ‘ no one gets a free lunch’ and so we pay a heavy price for conveniences like cheap fast foods, laziness and apathy, quick fix medications that only suppress symptoms without addressing the cause, etc.. Always question authority and do your homework.

  12. Andy D Says:
    April 17th, 2014 at 5:42 pm

    I myself do not trust Big government.They keep proving time and time again that lining their pockets is more important than our well being.Just type in FDA scandal and see what comes up, or try conflict of interest. These drugs for the most part are fast tracked with minimum research. Fast tracking was pushed through by the lobbyist. And the bean counters tell them what the potential risk is and they bring it to market. If you think otherwise your kidding yourself. This stuff will not go on or in my pets.

  13. Suzanne Says:
    June 2nd, 2014 at 8:08 pm

    This is my personal opinion but even before reading this article I refused to give any of my 3 dogs any flea preventative that they have to ingest. Personal choice and the people that have made the decision to treat their dogs with Trifexis and have had no side effects that’s great. No need to get defensive about the report. I believe that it will cause long term effects. I would rather use a topical which isn’t all together that healthy either.

  14. Holly Aydelette Says:
    August 4th, 2014 at 5:13 am

    We gave our dog Trifexis and he immediately started scratching. I agree with one lady; if they have to swallow flea medicine forget it! I tend to not want to try the new stuff and wait to see how it turns out before trying it.
    Say yes to trusted medicines!

  15. Tina Spears Says:
    August 11th, 2014 at 3:53 pm

    Very Concerned!! First dose of Trifexis given to my 132lb German Shepard last Wednesday, he vomited during the night. Saturday he had a seizure that lasted 5-10 minutes. It was horrible. I just spent $350.00 on Trifexis last week, and after everything I have read today, it’s going in the trash. Hopefully, my Shepard will not continue to have problems

  16. Mike Says:
    September 3rd, 2014 at 4:22 pm

    Our hearts are consumed with pain. We just lost our beloved dog Crown this morning. He was a very happy and extremely healthy 4 1/2 year old pup. We had taken him to the vet on 12 August for his checkup, and he received a clean bill of health. During the visit we needed to get him more heart worm preventative, usually heart guard, but the Vet convinced us of the benefits of Trifexis. He received his first dose of Trifexis that afternoon. During the time since then he seemed a little more sleepy and less playful, but we didn’t think too much of it at the time. He wasn’t sick and ate just fine. This morning we awoke to our sweet, active, loving and overly playful boy not coming to greet us immediately. We found him on his favorite spot looking to be asleep. When we tried to wake him he didn’t respond. He had stopped breathing. He was still very warm and looked to be in a deep sleep so we rushed him to the Emergency vet and they pronounced him dead.
    I am only now aware of the dangers with this drug and it is too late. The only thing that he had taken differently was this medication. He was extremely active and had a very good diet. He was 36 pounds and pure muscle. My family has been completely devastated by this.

  17. Pat Potesta Says:
    October 24th, 2014 at 2:05 pm

    I switched over to Trifexis several months ago. My dog goes to Banfield twice a year for his comprehensive exam. Always left there with perfect health care, until this last visit. My dog has developed a heart murmur. The vet says it’s common in that type of breed. I don’t believe them. The only thing I’ve changed in the last 7 1/2 years is his flea medication. I switched to trifexis at their recommendation. BAD MISTAKE…………….. I believe it is the trifexis. Now I have a sick dog.


Dr. Andrew Jones, DVM
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