Trifexis Side Effects on Dogs

A Flea Pill that Kills Heartworms, too?


Fleas and heartworms are two of the biggest concerns of dog owners and now Trifexis claims to treat both, but can it do it safely?

That’s what we’re going to do today: take a look at the ingredients and side effects to see if the benefits outweigh the risks.

How Does Trifexis Work?

Trifexis contains two medications, spinosad and milbemycin oxime. Spinosad is a neurotoxin that kills fleas by paralyzing them then killing them. The milbemycin oxime works to kill fleas and ticks as well as the worms.

You give your pet one Trifexis tablet per month. They’re dosed according to weight so be sure to get the one that’s appropriate for your dog.

Side Effects of Trifexis

Trifexis has several fairly common side effects including:

  • Vomiting
  • Itching
  • Lethargy
  • Diarrhea
  • Decreased appetite for a couple of days
  • Increased appetite or thirst

If vomiting occurs within one hour of administering, give your dog another whole dose.

There are also some rare side effects that, should they occur, warrant a call to your vet. They include:

  • Cough
  • Hyperactivity
  • Increased vocalization
  • Excess salivation
  • Skin irritation or redness

Trifexis may not be safe for use with breeding animals and extreme caution should be used with dogs with epilepsy.

Spinosad has been known to interact poorly with ivermectin so if you’re using a product containing that, such as Hartguard or IverGuard, speak with your vet prior to administering the Trifexis.

Increased instances of vomiting are reported in puppies less than 14 weeks.

Final Word

Heartworms are deadly to your dog. Rarely does an animal recover, and if they do, it’s a long, painful, expensive process. Trifexis may have some side effects but the most common ones are temporary and mild.

It’s our opinion that the risk of heartworms far outweighs the risk posed by side effects and we give Trifexis a thumbs up!

If you’ve tried Trifexis, please tell us about your experience in the comments section below.

5 Responses to “Trifexis Side Effects on Dogs”
  1. Phyllis says:

    I have three dogs that were given Trifexis yesterday. None of them will eat the tablet, therefore, I had to administer to them. One dog was fine with no reaction, another dog threw it up and I readministered; then she drooled for about an hour. The other dog, later that evening was somewhat lethargic and this morning, didn’t want to get up and seemed like she was drugged. She did eat and we went for morning walk but she came back and totally laid down and did not want to get up. This is the last time I will give her this medication along with the dog that was drooling. Very scary situation with dog that appears totally drugged.

    • denise tomlinson says:

      Did you feed them first before giving them the Trifexis? I made that mistake the first time I used it.I always feed them dinner then after dinner I give it to them.Now they are OK with it.I love it so easy for me.

  2. N Bear says:

    We have been giving our dog Trifexis for almost two years. We started giving her the pill when I became pregnant, because it was much safer than topical treatments for me and the baby. We have had absolutely no problems with it. I am so glad I found this product! Now, if it only worked on ticks!

  3. Dundi says:

    My dog is a 3 year old beagle mix. She was prescribed trfexis earlier this month because we are preparing to move overseas and she must be healthy with no fleas before she can fly. I gave her the trifexis with a meal on Friday, April 4. She had symptoms the next day. She was lethargic and trembling and wouldn’t eat. I took her for a walk on Sunday because she was eager to go out and had regained her appetite the next day. I’ve read other people’s stories that were similar to mine but when they gave their dog the second dose the symptoms were more severe. I’m afraid to give my dog a second dose because next month she will be in quarantine for three or more months in Hawaii.

  4. cd perkins says:

    Constant diarrhea, skin iritation, lethargy, and the pill smells horrible and i have to fight her to get it swallowed.

Tell Us What You Think!

Spam protection (register to skip this)

four + = 12