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.

One Response 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.

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