PetMeds® Comfortis Flea Control: Potential Side Effects

Filed under Dr. Dym's Vet Blog
Did you know that not all flea control products for dogs are applied to the skin? Many pet owners prefer oral administration of external parasiticides to avoid exposure of themselves to topical pesticides, which is why some dog owners prefer the ease of administering a chewable tablet such as Comfortis. Comfortis can control fleas up to one month on dogs, but it does not kill ticks

Comfortis kills fleas within 30 minutes and lasts for up to one month. In my experience common client concerns include lack of efficacy against other external parasites such as ticks, as well as the need for written prescription from the veterinarian.

One of my concerns with Comfortis is the occasional wide range of side effects including vomiting and/or diarrhea and various neurological reactions ranging from incoordination, trembling, and seizures.  It’s for these reasons that I generally prefer using other flea and tick products in my practice such as Frontline Plus or Advantage II.

However, clients do report mostly high satisfaction with this product, with the exception of these occasionally severe side effects.  It is also important to still treat the environment for fleas, as well as incorporate additional measure to help control other parasites such as ticks if using Comfortis.

Read Related Posts on PetMeds® Blog:

  1. PetMeds® K9 Advantix II: Flea Control for Dogs
  2. PetMeds® Frontline Top Spot Flea Control
  3. PetMeds® Are Topical Flea & Tick Pet Medications Safe?
  4. PetMeds® Heartworm and Flea Control in One: Sentinel
  5. Pet Reactions to Topical Flea Products


  1. Tash bannister
    Posted November 20, 2011 at 5:16 pm | Permalink

    im doing a speech on comfortis and im wondering if its better than a flea coller can you help me

  2. tess haunch
    Posted November 20, 2011 at 5:20 pm | Permalink

    I LOVE DOGGIES HE HE HE AM I CRAZY and i dont want them to suffer of fles my poor darlings so im going to use comfortis is it good or should i use a pet flea collar

  3. Dr. Michael Dym, VMD veterinarian
    Posted November 20, 2011 at 7:25 pm | Permalink

    Comfortis does work better than flea collars in most cases.

  4. Tash Bannister
    Posted November 21, 2011 at 6:07 pm | Permalink

    thanks so for whole body flea treatments use comfortis

    but neck treatment you can use flea collars if you want for good results cool any other information for me ?

  5. crack genius
    Posted November 21, 2011 at 6:10 pm | Permalink

    hi im soooo crazy hey i take drugs do you hey you should see me some time and hang out in an alley together eh whats your phone number and dont worry about your question i love you i know im awsome arnt i

  6. crack genius
    Posted November 21, 2011 at 6:19 pm | Permalink

    oh well you can get married at the age of ten i love you im asking for your hand in marrige and yes you are gonna be my wife hahahahaha

  7. Tess Haunch
    Posted November 21, 2011 at 6:22 pm | Permalink

    hehehe yes ill marry you i love you to

  8. petmeds
    Posted November 21, 2011 at 7:20 pm | Permalink

    this is unacceptable you two i have the right to ban you please be sensable

  9. Dr. Michael Dym, VMD veterinarian
    Posted November 21, 2011 at 8:27 pm | Permalink

    I am not fan of using flea collars when pets are on other pesticides such as comfortis.

  10. Tash Bannister
    Posted November 22, 2011 at 9:57 pm | Permalink

    thanks but have you Seen any side effects yourself and has THE CUSTOMERS BEEN UPSET WITH THE PRODUCT

  11. Dr. Michael Dym, VMD veterinarian
    Posted November 22, 2011 at 10:31 pm | Permalink

    I have not seen many side effects on the few cases I have used it in practice, but have heard and read of side effects.

  12. Tash Bannister
    Posted November 24, 2011 at 9:30 pm | Permalink

    yes ive heard about seizures and diarrhea but yes thankyou for your information in the future i will use that product

  13. Dr. Michael Dym, VMD veterinarian
    Posted November 25, 2011 at 7:45 pm | Permalink

    You are very welcome. Spread word to your family and friends a about this service.

  14. laura
    Posted March 31, 2012 at 8:45 am | Permalink

    Within a few hours of giving dog medicine she became very lethargic. Normally she is very active and plays constantly but not after this. She just laid around for about 24 hours finally started getting some energy back slowly. Wow bad bad smell and horrible breath to go along with this medicine which lasted about 3 days. The worst thing I have ever smelled. Will NOT be using this again.

  15. Dr. Michael Dym, VMD veterinarian
    Posted March 31, 2012 at 3:16 pm | Permalink

    Occasional side effects with any pesticide may be seen. Thanks for sharing and I agree on not using this again in your animal companion.

  16. Cynthia
    Posted July 25, 2012 at 3:32 pm | Permalink

    Taking my two dogs for flea control. My vet uses confortis. I have heard about bad side affects from this med. What is your opinion?

  17. Dr. Michael Dym, VMD veterinarian
    Posted July 26, 2012 at 1:37 pm | Permalink

    Oral comfortis is very effective for flea control. Like any pesticide products rare side effects can be seen in some animals.

  18. Linda
    Posted August 10, 2012 at 11:30 pm | Permalink

    I gave our German Shepherd Comfortis tonight. Just returned from the Emergency Vet. Within a half an hour after eating the medicine, her back legs went out. She couldn’t walk. I’m sick over this. I’m praying she will be better \in the next couple days\ as the emergency vet said, as the meds get out of her system. They had to sedate her to do X-rays because we thought she’d broken her leg or her hips were in trouble. So, it remains to be seen. No…nothing broken, hips fine. Coincidence? I think not. I’m certain it was the COMFORTIS. Maybe she’s one in a hundred who gets serious side effects, but she’s one in a million to me and I am broken-hearted that she trusts me and I gave her this poison.

  19. Dr. Michael Dym, VMD veterinarian
    Posted August 11, 2012 at 5:00 pm | Permalink

    Sorry to hear about reaction to the comfortis. Consider alternative topical product and/or natural flea control or

  20. ginny
    Posted September 13, 2012 at 3:33 pm | Permalink

    Our dog was only 6 when he did last year from liver failure. We had him on Comfortis for most of his life. Has there been any association between Comfortis and liver problems? Our last dog (different breed) lived to 14 and we were giving him frontline.

    The Comfortis worked great as we live in a hot climate that produces both fleas and ticks. But before getting another dog, I’d like to have some answers to why our dog died at a relatively young age.

  21. Dr. Michael Dym, VMD veterinarian
    Posted September 13, 2012 at 8:45 pm | Permalink

    Any topical or oral pesticide has the potential to cause problems long term with organ function but hard to prove or disprove. Also other toxins in environment or food could be involved as well.

  22. Linda
    Posted September 13, 2012 at 9:02 pm | Permalink

    No, not this time. We are very careful with our pets. My dog was running for a frisbee before she at this pill…perfect health. Had just had a physical recently. Three years old…in her prime. 15-20 minutes after eating this pill, her legs gave out! ABSOLUTELY NO QUESTION AT ALL. It wore off, thank goodness. Company realized issue. Reports were made to FDA. Company was concerned and helped pay emergency bills, etc. They realize this is a severe possible side effect, but I didn’t. My fault, as the consumer…I didn’t research it enough.

  23. Dr. Michael Dym, VMD veterinarian
    Posted September 13, 2012 at 9:49 pm | Permalink

    Thanks for sharing. Sorry for your dog’s experience with comfortis.

  24. Charles
    Posted October 11, 2012 at 9:13 pm | Permalink

    I gave my dog comfotis and she immediately started scratching and her skin was very red. i thought she had got into something in the yard so i treated the entire yard with weed killer and pesticdes. She still has the same problem only worse. Took her to the vet today and they say it’s her thyroid. Didnt have any problems until she started taking this. Have you seen any side effects such as thyroid during use of comfortis?

  25. Dr. Michael Dym, VMD veterinarian
    Posted October 12, 2012 at 6:22 pm | Permalink

    I have not heard of comfortis causing any thyroid problems in dogs.

  26. Posted November 11, 2012 at 2:31 pm | Permalink

    I am using Comfortis for the 2nd month with no side affects, but limited success. I increased the dosage the 2nd month, because my dog is borderline 40 lbs, still no side affects, but she is still scratching and chewing, however, not as much. I have never had a flea problem until this year and am trying to vacuum and keep the house free of any larvae, eggs, that may be inside. Still
    the scratching and chewing is driving us, both, nuts.
    Any suggestions on anything I can put down in the house and bedding to help kill any fleas that may are hatching after I started treating her? Or should I try a topical flea killer on the dog instead of the Comfortis?

  27. Dr. Michael Dym, VMD veterinarian
    Posted November 11, 2012 at 4:44 pm | Permalink

    I would try oral program and capstar from 1800petmeds. Also consider flea busters for home which you can find on line.

  28. tash
    Posted November 11, 2012 at 8:46 pm | Permalink

    yes i have fleas and i am sooo itchy

  29. tash
    Posted November 11, 2012 at 8:53 pm | Permalink

    hi kayla

  30. jasmines on crack
    Posted November 11, 2012 at 8:54 pm | Permalink

    Lol funi just werd

  31. jasmines on more cra
    Posted November 11, 2012 at 8:58 pm | Permalink

    she awsome

  32. tash is on crack
    Posted November 11, 2012 at 8:58 pm | Permalink

    derr brain

  33. tash
    Posted November 11, 2012 at 9:00 pm | Permalink

    kayla stop it u r mean
    i hate you :( !!!!!!!!

  34. Gangnam style
    Posted November 11, 2012 at 9:20 pm | Permalink

    :( lol ae it was funi

  35. Nancy Chambers
    Posted November 14, 2012 at 10:20 pm | Permalink

    I gave my dogs Comfortis for the first time and one has horrible bloody diarrhea for three days. Vet has prescribed Pana something (liquid) and nothing has changed. Other dog is extremely lethargic and won’t eat. If they do live thru this, I will NEVER use it again and if they don’t make it… I wish I could sue. I am furious and scared.

  36. Dr. Michael Dym, VMD veterinarian
    Posted November 15, 2012 at 12:31 pm | Permalink

    If symptoms persist over a few days see vet again for more supportive care. Side effects should wear off within a few days.

  37. freddiella monters
    Posted November 25, 2012 at 2:47 am | Permalink

    i gave my dog comfortis and a few hours later she started throwing up and had horrible diarrhea for ages
    comfortis seems to have a lot of problems and i will not be using it again

    you should also tell those silly kids to stop writing those comments on they are taking advantage of your blog !!

  38. Dr. Michael Dym, VMD veterinarian
    Posted November 25, 2012 at 7:54 pm | Permalink

    Thanks for sharing your wonderful and touching story.

  39. Dr. Michael Dym, VMD veterinarian
    Posted November 25, 2012 at 7:55 pm | Permalink

    Some pets can react to comfortis. Thanks for sharing your thoughts. Consider natural flea control if chemicals causing problems such as wondercide or cedarcide

  40. natasha
    Posted December 4, 2012 at 5:59 pm | Permalink

    i like boys

  41. mrs fenemor
    Posted December 6, 2012 at 6:54 pm | Permalink

    natasha get off this site im dieing to havee explosive diroheea soon and i need you here to comfort me

  42. Stephanie
    Posted December 10, 2012 at 12:49 pm | Permalink

    I gave my 14 year old AmStaff her first dose of Comfortis almost 24 hours ago and I am happy to report that she did not have any visible side effects and even better than that, she doesn’t have any fleas! When we lived in NY Frontline was all that was needed and it was moreso for ticks. I had never seen a flea before moving to FL. Frontline, baths and herbal remedies were to no avail. Comfortis seems to be working like a charm.

  43. Dr. Michael Dym, VMD veterinarian
    Posted December 10, 2012 at 1:41 pm | Permalink

    THanks for sharing. Comfortis is usually quite effective orally. Good luck in this tough state of Florida with fleas, etc.

  44. Holly Holderman
    Posted December 31, 2012 at 2:51 am | Permalink

    My older dog was given comfortis on Dec 28th after dinner.

    He started throwing up at 2:45am Saturday morning.

    He is so sick right now, and we can’t seem to make him feel any better.

    Have been to the vet 3 times in 3 days…sub q fluids, cerenia
    Homeopathy, etc.
    His liver & kidney #’s are normal waiting on pancreatitis

    Hoping he will turn around…but I am worried sick myself.

    It’s been 48 hours, and its not getting any better.

  45. Dr. Michael Dym, VMD veterinarian
    Posted December 31, 2012 at 11:30 am | Permalink

    HI Holly: Sorry to hear of your dog’s problems after comfortis. Probably best to consider IV fluids at vet office for a few days until symptoms calm down. What type of homeopathy was given? You may want to consult with a classical homeopath, which prescribes remedies based on constitutional symptoms. To learn more see

  46. Pam
    Posted April 14, 2013 at 5:22 pm | Permalink

    I used Comfortis for my 3 German Shepherds. Loved it at first, no fleas whatsoever. After a few months of taking it, all three started having seizures. They all started to refuse to eat it. Took them off the Comfortis, and it took 6-8 months before they quit having the seizures. Now just trying to find something that will keep the fleas away. Going to try the Seresto Collar. Hope it works as well.

  47. Dr. Michael Dym, VMD veterinarian
    Posted April 15, 2013 at 10:12 am | Permalink

    Try topical revolution from 1800petmeds.

  48. Cathy
    Posted April 18, 2013 at 11:55 am | Permalink

    I just bought a mini schnauzer (8weeks old) and was told not to use oral flea control as they cause cancer. Is that true? I’ve been giving my Boxer oral flea control for years, she seems fine but this comment scared me.

  49. Dr. Michael Dym, VMD veterinarian
    Posted April 18, 2013 at 10:03 pm | Permalink

    Most oral pesticides such as comfortis are fine to use in most dogs. In sensitive breeds, chronic pesticide use may be linked with chronic diseases, although hard to prove.

  50. lorrie
    Posted April 26, 2013 at 2:42 pm | Permalink

    the comfortis could be causing the scratching, have you read these other comments? you should.

  51. lorrie staley
    Posted April 26, 2013 at 2:46 pm | Permalink

    oh my gosh, I just thought my dog was going to die. she has never had a seizure in her life and I gave her one of these comfortis pills this morning for the first time and she just now had a huge seizure. I really thought she was going to die. and now she can’t hardly get up or stand up. I have been crying my eyes out and I just feel terrible. she also peed all over the floor. it seemed like she was never going to come out of it. I hope she can walk tomorrow. terrible just terrible. I have to take my finals next week and now all I am going to be able to do is think about her.

  52. Dr. Michael Dym, VMD veterinarian
    Posted April 28, 2013 at 10:52 pm | Permalink

    Hi Lorrie. Consider natural flea control such as Also if health issues persist, consider working with homeopathic vet

    Posted May 5, 2013 at 6:52 pm | Permalink

    I have had my Senior Doxie on Comfortis for three years and all year long. i see the relief that my dog gets in a short period of time and she stops scratching and chewing. i have not seen any bad side effects with this oral medication. it is far worse to expose the dog to flea shampoo and then a toxic flea collar and still see fleas. my vet sells me the pills and matches the doseage to her weight. i reccoment this to dog owners.

  54. Dr. Michael Dym, VMD veterinarian
    Posted May 5, 2013 at 10:50 pm | Permalink

    Thanks for sharing.

    Posted May 6, 2013 at 1:54 am | Permalink

    Waching your dog have a siezure is frightening. They cannot tell us that they feel odd, or their stomach is upset.
    My spelling was terrible from my last posting. Dogs and cats bring fleas into the house and we carry them in on our shoes. The key I think is to stay on top of them from the start. My dog got fleas after I kept a friends dog with me for four days while the owners went to a cutting horse competition. Harley had fleas and I did not think about it. I let him sleep in my bed with me and my dog. After I returned Harley I spotted the fleas on my dog. I did the flea shampoo thing and did not know Comfortis existed. My neighbor came over and we sat on the floor picking fleas off of my dog and dropped them in a cup of water. Fleas cannot swim so they sank to the bottom of the water cup. I am looking for a natural flea spray that I can use on my dog and on my bed. Any ideas?

  56. sam pawley
    Posted May 6, 2013 at 10:19 pm | Permalink

    I have heaps of fleas please help me i like little children

  57. Dr. Michael Dym, VMD veterinarian
    Posted May 6, 2013 at 10:51 pm | Permalink

    Try flea free from 1800petmeds Another great natural product I have found for fleas is

  58. Posted May 7, 2013 at 10:29 am | Permalink

    I just purchased Trifexis, it’s a monthly tablet dogs/cats take to kill fleas, protect the heart and kills any intestine worms. Gave both my dogs this last night, checked them this morning and the fleas are DEAD!!! Amazing product. You have to be careful with the others because they kill the flea larva but not the flea…the flea will continue laying eggs and you will never get rid of them. Trifexis is expensive but well worth it.
    This is where I bought mine from

  59. Dr. Michael Dym, VMD veterinarian
    Posted May 8, 2013 at 11:24 pm | Permalink

    Trifexis is excellent product but do need written script for it from vet. Available economically at 1800petmeds.

    Posted May 8, 2013 at 11:59 pm | Permalink

    The first few times that I pilled my Doxie Gretchen with Comfortis she gobbled the tablet down like a starved animal. I had to start asking her to do something for her “treat” and that lasted..a while. I progressed to wrapping the pill in cheese. as she watched. That worked once. I bought liver sausage and stuck her pill in that for a few months. It has gotten to the point that her and I struggle to get the pill in her mouth and I hope she swallows it. She gets a real treat if I do not see her hack the pill up onto the floor! I have wormed a horse with less trouble. I end up all sweaty and my hair sticking up. She is 15 years old and thinks she is Alpha to the planet. What gives?

  61. Dr. Michael Dym, VMD veterinarian
    Posted May 9, 2013 at 12:27 am | Permalink

    I am concerned that her body may be reacting to the comfortis pill when I see a pattern like this, especially in a breed like a doxie which is very sensitive to drugs, chemicals, vaccines, etc. She is probably learning through repetitive doses that she does not feel so well after taking it, which can be seen with any pesticide in elder animals. Maybe consider an alternative flea control product in pet this age, even a natural option like flea free from 1800petmeds.

  62. B
    Posted May 23, 2013 at 4:21 am | Permalink

    I gave my 2 dogs and 2 cats comfortis 2 weeks ago. One cat threw up, the fleas seem to be gone but today one dog started having seizures ..4 so far!! I’m just sick about it !! This was a totally healthy dog!!! Does she have a permanent problem or will it go away ??? What can I do for her ??

  63. Dr. Michael Dym, VMD veterinarian
    Posted May 23, 2013 at 11:03 pm | Permalink

    I have seen rare neurological reactions to any of the oral or topical pesticides. hard to say if seizure disorder was caused by product or just a pre existing tendency was already there. Best to see vet for exam and evaluation to see if anticonvulsant meds may help. Also could consult with a homeopathic vet to try and raise level of health over time. To learn more about homeopathy see as well as my website

  64. Posted June 7, 2013 at 4:56 pm | Permalink

    I just gave my dogs Comfortis today and within an hour 2 of them started throwing up, not just once, but 5 or 6 times (each). I wish I had never heard of this medication. I have also read reviews and experiences where many dogs even died from Comfortis. My recommendation: Do NOT give this to your dogs.

  65. Dr. Michael Dym, VMD veterinarian
    Posted June 7, 2013 at 5:43 pm | Permalink

    HI Sue. Sorry foryour experience with comfortis. I certainly would not use it again in your case.

    Posted June 7, 2013 at 10:03 pm | Permalink

    My senoor Doxie does well on Comfortis however I am wondering if she is building up a tolerance to the drug. I find a flea or two on her. i purchased flea busters and should get it in a few days. I also purchased an organic flea powder that can be used on my dog and her bedding. She starts her day with a benedryl type pill that gives her relief from the itching. My Vet says that she is allergic to the flea bites. I have a topical spray that I use to stop her itching in one area. I am interested in massage therapy for my senior doxie….just because I love her. BTW flea collars are highly toxic!

  67. Dr. Michael Dym, VMD veterinarian
    Posted June 8, 2013 at 1:10 pm | Permalink

    Thanks for sharing. Also consider natural flea product like

  68. Amanda
    Posted September 8, 2013 at 6:31 pm | Permalink

    I gave both my dogs comfortis but for some reason only lasted about three weeks then I seen the dogs scratching and spotted fleas on them. Did I maybe not give right dosage I have a bichon fries and an English springer spaniel

  69. Dr. Michael Dym, VMD veterinarian
    Posted September 9, 2013 at 11:29 pm | Permalink

    in some cases of heavy infestation, pets need to be dosed sooner than one month. Also remember to treat the home for fleas as well.

  70. Posted September 24, 2013 at 2:57 am | Permalink

    We have found just the opposite using Frontline or Advantage, both cause seizures for our Aussie Shepard so we are trying Comfortis for the first time, we’ll see how this plays out

  71. Dr. Michael Dym, VMD veterinarian
    Posted September 24, 2013 at 6:52 am | Permalink

    Every pet is an individual with unique sensitivities.

  72. Posted October 2, 2013 at 11:00 pm | Permalink

    I gave my 4yr old Chihuahua her first dose of Comfortis @ 4 pm yesterday. She got rather hyper and paranoid … She followed me everywhere. She also ate a lot. Instructions said give with a full meal but she kept eating afterward. Today she had a small normal consistency poop, and this evening some diarrhea. Otherwise she is active and happy. I hope it works since she gets FAD really bad every year when it gets warm and we have to go to the vet for Simplicef and Temeril-P.

  73. Dr. Michael Dym, VMD veterinarian
    Posted October 3, 2013 at 11:45 pm | Permalink

    Every pet different with oral or topical pesticides. If side effects occur again next month, then best to change to different preventative such as program or topical revolution

  74. Kerri Howard
    Posted November 19, 2013 at 5:46 pm | Permalink

    Can you give your animal a flea bath on top of comfortis. ?it has been about 45min since I gave it and the poor thing has tons of fleas.

  75. Dr. Michael Dym, VMD veterinarian
    Posted November 19, 2013 at 6:32 pm | Permalink

    You can give flea bath at same time as comfortis.

  76. christine
    Posted March 15, 2014 at 1:44 pm | Permalink

    when in southern california, vet prescribed Comfortis for 10 lb and 15 lb chihuahua mixes. i was amazed how much they scratched soon after application, and was told it was the fleas coming out of their skin… already dead… and that this would kill adults and larvae and eggs alike. i put the pill at the back of their tongues and held their muzzles shut until i knew they’d swallow it… pretty easy with the learned technique, and very clean.
    … since then have moved to the mountains of arizona, where vet prescribes topical Frontline. i’m not sold on this product. just returned from visit to the beach in so cal, and came home with poor itchy pup. an oatmeal bath has not eased his discomfort.
    … it’s been only 2 or 3 weeks since last application of Frontline. i’m here to order Comfortis once again. i’ve never experienced side effects mentioned by others (my sincere sympathy), and have visible results within hours of dose… even though it’s a bit disconcerting to see them scratch like crazy for a while.

  77. Dr. Michael Dym, VMD veterinarian
    Posted March 17, 2014 at 6:05 pm | Permalink

    I dont have problem with comfortis in most cases. On occasion side effects can be seen with any pesticide. You will need written script from your vet to order the comforts

  78. ConcernedDogMom
    Posted April 21, 2014 at 2:10 pm | Permalink

    I have an Epileptic 3 year old Aussie whom I can not give him any flea meds that contain Comfortis. He has never had a Flea before but lately I have noticed a couple and although I am quick to catch them, I know the risks & dangers of having even 1 tiny flea. I have been looking everywhere online, in pet stores as well as asking my VET. and I can’t seem to find a resolution. I need help finding a natural flea product where it won’t cause my baby to go into seizures every month. Can anyone Help please? Thanks

  79. Dr. Michael Dym, VMD veterinarian
    Posted April 26, 2014 at 3:58 pm | Permalink

    Consider working with a holistic veterinarian on improving your dog’s overall health so not so attractive to fleas. See my website for more information. Many holistic vets do offer phone consultations. An excellent natural flea product is

  80. christine
    Posted April 27, 2014 at 5:24 pm | Permalink

    i had no adverse reactions and much less scratching after this mid-april dose of comfortis. i still prefer it to frontline. will report back if any bad experiences… otherwise, i’m sticking with comfortis because it seems to work great for my pups.

  81. Dr. Michael Dym, VMD veterinarian
    Posted April 28, 2014 at 2:47 pm | Permalink

    Thanks for sharing

  82. JV
    Posted June 4, 2014 at 9:28 am | Permalink

    Add me to the list of having a dog who quite likely had an adverse reaction to Comfortis. My 13 year old Border Collie had severe vomiting and tremors approximately 5 days after receiving Comfortis. The tremors became uncontrollable and progressed to the point where she could not walk. We really thought we were going to lose her. After rushing her to the ER to be stabilized and monitored, along with a follow-up consult with a neurologist, we were unable to make a positive dx. The one new factor in her life was Comfortis. After taking her off Comfortis, she is now completely normal 3 months post the tremors/neurologic episode. Was I informed by the neurologist of a possible connection to Comfortis? Nope, he only wanted to do a spinal tap and an MIR….Positive conclusion? Nope. Will I ever give her Comfortis again. H NO!!!

  83. mandy
    Posted July 2, 2014 at 10:25 am | Permalink

    We gave our lil 20 lb dog comfortis two days ago shes normally very active shes only 4 yrs old. She slept and layed around for two days!!!! She had a bad odor coming from her skin we are NEVER giving her this again!!!!!

  84. mandy
    Posted July 2, 2014 at 10:27 am | Permalink

    She was also trembling.

  85. Dr. Michael Dym, VMD veterinarian
    Posted July 4, 2014 at 6:31 pm | Permalink

    Sorry to hear about this Mandy. Hope she feels better soon.

  86. tammie
    Posted September 24, 2014 at 1:49 am | Permalink

    I gave both my dogs a cap star….then bathed them a few hours later, then before bed I gave them both a comfortis. 6 hours later the little one is fine! The larger female has been out twice and acting like she can not get comfortable. Has this can’t get comfortable feeling for over one hour. Plus during her time of going outside she has had 3 bowel movements. She is just not acting right.

  87. Dr. Michael Dym, VMD veterinarian
    Posted September 24, 2014 at 10:34 am | Permalink

    Could be reaction to too many meds at once. She should be fine in a few hours. If symptoms persist or worsen, see vet for evaluation

  88. Tia Chambers
    Posted October 13, 2014 at 9:44 pm | Permalink

    I gave my 2 yo dog comfortis 2 weeks ago. After giving it to her I noticed she was having a difficult time walking, even became paralyzed for a couple hrs. She normally is very active and intergetic. It’s been 2 weeks and she’s still having difficulty getting around. I have taken her to the vet but they brush it off as being a spinal issue and tell me comfortis won’t cause these complaints. know this is a side effect, but was wondering if she will always have trouble now, or if maybe this will wear off with time.

  89. Dr. Michael Dym, VMD veterinarian
    Posted October 14, 2014 at 3:59 pm | Permalink

    Hi Tia. Hopefully it will wear off with time. I do agree with you, any topical or oral flea/tick pesticide may cause neurological issues in some sensitive patients. I would consider consulting with a holistic vet. to learn more about homeopathy see the booklet on the website and my website . Many homeopathic vets do offer phone consultations.

  90. Julia
    Posted October 19, 2014 at 12:48 am | Permalink

    I used comfortis on my golden puppy 4 times starting from 16 weeks old. The first 3 times he was absolutely fine. Last time he got the pill was 5 days ago. The next morning he started vomiting with yellow liquid, he stopped moving, eat and drink, we took him to the vet the next day, they made fluids, ton of injections and gave medication for using at home. He felt better right after procedure but he still didn’t drink or eat and started throw up in the evening. We took him to the vet again, they did the same and the result was the same. He’s continuing vomiting and refusing eat and drink. I don’t know what to do, it’s 4th day without food, so I literally push can food in his throat, and in couple ours he throws up this food and medication. Veterinarian obviously can’t help, I know for sure that it’s happening because of comfortis cause that was the only difference in his routin. Please help me somebody who had this problem! What else can I do to save my puppy? He’s dying in from me

  91. Dr. Michael Dym, VMD veterinarian
    Posted October 19, 2014 at 3:16 pm | Permalink

    There may be another condition in a young puppy like this such as an undiagnosed foreign body. I would ask your vet to send the x rays out for a board certified radiologist to read. Barium swallow x ray studies may also be helpful here. If not already done, I would recommend a FULL CBC/chemistry blood profile to make sure nothing else going on. If your vet stuck, then referral to vet internist in your area or specialist may be worthwhile.

  92. Holly
    Posted January 13, 2015 at 12:16 am | Permalink

    DO NOT GIVE your animals Comfortis or Trifexis (which has Comfortis). My dog ended up in the ER and had to be put on oxygen. If i had not taken him, he would have DIED over this medication! He could not breathe and was trembling. We took him to the ER and he passed out on the table and had to be rushed to the back for oxygen and add’l meds to save him. Wish I had read reviews before giving it to my dog! Look at all sites for all bad reviews on this medication and choose something else! Your dog or cat will love you for it!!

  93. Amy
    Posted March 19, 2015 at 2:17 pm | Permalink

    If cat only threw up over an hr after ingestion will it still work? I hope some got into his blood. He itched like crazy for an hr or two after ingestion and maybe longer. Then some time during our sleep he threw up lots of kibble and fur. This morning he itched and shook once but seems settled. I am really hoping the vomit was from the sensation he felt after it was in his blood and NOT that the pricey pill was lost in the vomit on the floor! Expensive flea collar, Revolution, nor FrontLine worked.

  94. Ashley
    Posted April 11, 2015 at 12:09 am | Permalink

    Anyone else’s dog get MEAN om confortis?
    I gave my 8 year old dog confortis today for the first time in a about 3 years…i just got her back from my ex husband about 3 months ago. I also gave it to my Pyrenese who gets it all the time. My two dogs are the best of friends….never been in a fight.
    Well about 3 hours after I gave them the confortis I went to check on them outside. My older dog daisy was acting weird…she was growling at my Pyrenese and her back legs were shaking and her muscles were twitching on her back legs. I got up to bring her to my shed to look her over because she was acting weird trembling and growling!!!! As soon as I turned around the dogs were fighting…it was terrible and so scary! It was like two lions fighting.
    Neither I my dogs are aggressive…AT ALL!!!
    ****this confortis made my older dog go crazy and be mean! She has never growled at anything and has definitely never trembled!!!
    Anyone else’s dogs get mean on confortis?

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