Anybody can have a reaction to any medication. The way I look at it, if your dog never has a problem with Trifexis, then it may be fine.
However, if your dog has the least change in behavior, anything out of the ordinary, anything at all, then I would discontinue immediately.
These changes can include vomiting, diarrhea, laying around for a day or two, or just seeming a little “not right.” Some people and their dogs have great luck with the medication, some people don’t; The dogs who are not doing well with it should not continue simply because it’s wonderful not to have to put something sticky on the back of their dog’s neck. I do believe that there are dogs who have taken Trifexis and become ill and died. In fact, I have a little dog under my care now who is touch and go, due to Trifexis. But so far so good.
Fortunately, because I practice a slightly different kind of veterinary medicine, I don’t just intuitively believe everything that comes from a drug company is safe. For my patients who have any questions about the safety of Trifexis in their dogs, I have no problem with a two second check in the office when you come to buy flea and heartworm medicine: I am more than happy to muscle test your dog and make sure Trifexis is safe. If not, I’ll be happy to recommend an alternative so you can keep your baby protected and keep your house free of fleas.