Side Effects of Trifexis

There has been some controversy about the side effects of Trifexis. Several dog owners have reported that this drug caused or contributed to the death of their pets. Though other studies say that the claim is unproven and undetermined.

What is Trifexis?

Trifexis for dogs is a monthly chewable tablet administered to dogs. The ingredients are 270 mg of Spinosad and 4.5 mg of Milbemycin Oxime. The tablet is available in beef flavor. The flavoring is made from hydrolyzed soy and pork-based proteins. 

The dosage prevents flea infestation and kills them. It is also a preventive, control and treatment for whipworm, hookworm and roundworm and heartworm disease. 

Trifexis can be administered to puppies from 8 weeks of age. They should weigh 5 pounds and above. Visit your veterinarian to perform the test annually.  Like any medicine, this one too has side effects. 

Uses of Trifexis

side effects of trifexis in puppies

This drug is a combination of spinosad + milbemycin oxime. It is effective in killing fleas and prevents further infestation. 

The manufacturers claim that this medication kills fleas in 30 minutes of being administered. It eliminates all the fleas within four hours. 

A single dose of this chewable tablet is effective for 30 days. It protects the canine from intestinal parasites such as heartworms. It also treats and controls whipworm, adult hookworm, and roundworm infections. 

To be on the safe side, continue administering the dose for at least 3 months following the last exposure to mosquitoes.

Dosage of Trifexis

To prevent any side effects of Trifexis we should know about the dosage. Any drug when administered in excess causes side effects. To prevent any degradation of the medicine it should be stored in dry and cool places between 68° – 77°F.

The dosage depends upon the weight of the dog. Each pack indicates the weight of the dog and the dose. A single tablet contains 270 mg of Spinosad and 4.5 mg of Milbemycin Oxime. This dose should be sufficient for a 10 – 20-pound dog. A dose of a single tablet will remain effective for 30 days.

Side Effects of Trifexis

side effects of trifexis itching

The most common side effects of Trifexis is vomiting. There are several other side effects you should be aware of. Most of the time accompaniment with sufficient water and food should prevent them. If they cause discomfort to your dog then see the veterinarian. The most common side effects are. 

  • redness of the skin and ears
  • itching
  • lethargy 
  • loss of appetite
  • diarrhea

The adverse reactions to Trifexis can be depression, pruritus, trembling or shaking, anorexia, ataxia, hypersalivation, and seizures. 

How to Prevent Side Effects of Trifexis?

To spare the pet any discomfort discuss the medication you are already giving your dog. The veterinarian will be able to tell you if they will react with the Trifexis

It is very important to discuss the other medication your pooch is receiving, especially if the dog has epilepsy. Certain conditions may make Trifexis unsafe for your pet. Do not give these tablets to pregnant bitches and puppies younger than 8 weeks. 

If there is an allergic reaction it could lead to anaphylaxis. if you see any reactions contact the veterinarian.

FAQs on Trifexis

common side effects of trifexis

What Are the Benefits of Trifexis?

Trifexis is an oral tablet administered monthly to prevent fleas and other types of worms that affect canines. The benefit is that you are covered for so many ailments in one dose. Besides, t continues to remain effective for a month.

The other benefit is that the dose begins to take effect in 30 minutes. It is 100% effective in 4 hours. 

Dogs with allergy and dermatitis begin to show improvement in papules, erythema, alopecia, scaling, pyodermatitis, and itching. This is the result of the elimination of fleas. 

What Potencies or Strengths is Trifexis Available in?

Trifexis is available in 5 strengths. Each tablet is designed to administer a minimum dose of 13.5 mg/pound or 30 mg/kg spinosad and 0.2 mg/lb. or 0.5 mg/kg of milbemycin oxime. The mg/lb. or mg/kg refers to the dog’s weight in pounds or kilograms.

At What Stage of Their Life Does Trifexis Kill the Fleas?

The spinosad in the Trifexis kills fleas before they can lay eggs. If there is a severe infestation due to the environmental conditions the fleas may persist. This persistence after the administration of the dose may be due to the emergence of adult fleas from pupae. Even so, a 98 – 99.8% reduction is seen over 3 months. There is also an improvement in other conditions like itching, alopecia, scaling, etc.

Is Trifexis safe for breeding dogs?

Consult your veterinarian before giving Trifexis to the breeding female. It is safe to give this medicine you the male dog that intends to breed. 

Is Trifexis Effective on Heartworms?

Trifexis prevents heartworm disease by killing L3 and L4 larval stages that may develop after the dog has been bitten by an infected mosquito. These are the stages before the worm molts to the final stage to become an adult. It does not kill adult heartworms.


  1. Julie Bergman says

    Just want to tell you our precious shih tzu Peppy suffered so long with itching and constant licking himself to the point of licking the hair off. We took him off trifexis and the itching and licking stopped. We are a happy family now❣️

  2. No way I would ever give this to my dog. My best friend gave her dog Trifexis on Friday and he was dead on Sunday. He was not poisoned he had no other underlying issues. He was perfectly heatlthy and dead within 48 hours.

  3. Deborah McKenzie says

    I’m wondering if this is what’s causing my granddog to have seizures. Further, it makes me wonder if this could have caused his collapsed trachea.

    • Davis massey says

      I have been wondering about this med causing seizurese . Our little Banjo started having them. Vet has him on meds now for it. But I believe its this worming meds so I Google it. I now see this wormer can cause it. Our other pup often jerks like jumping whike sitting or lieing down. I just read your response about the seizures. I’ll be looking for something else for our pups

  4. Jim jenkins says

    Julie: stop the trifectus. ASAP. IT CAUSED SEISURES AND DEATH IN MY MINI SCHAZZER. In my opinion!! Spelling?? I know !-

  5. HAL Smith says

    HAve taken my dogs off of this . Its been vomiting for a few days after every dose for one of my dogs In the other dog , it has been hairloss to the point of looking grungy. Of course my vet denies the problems with the drug, but I know what has happened to them since being put on the Trifexis.

  6. HAL Smith says

    I have taken both dogs off this medicine. One has severe vomiting a couple days after taking it. The other dog has lost a lot of her hair since being on this drug. The vet says the drug does not do this….. but it started after taking this medicine for a while.

  7. HAL Smith says

    taking both dogs off trifexis. problems every month with vomiting to the point of haveing to go to vet for meds to stop vomiting

  8. Beverly Marnell says

    Please don’t give this to your dog! I gave it to my three dachshunds and within an hour one of them was very sick. He ended up in an emergency vet with a severe case of pancreatitis that left the pancreas permanently damaged. It has caused him to become diabetic. He is also suffering from liver and gallbladder issues. Two of the dachshunds have suffered neurological problems. They all had elevated liver enzymes and enlarged livers. I have spent at least 45,000 in hospital bills!!! It is a disgrace that this medicine is still on the market. It contains Spinosad. The Spinosad website clearly states that it is not to be ingested. I read that Spinosad is used to spray bugs. It causes bugs to have central nervous problems and then they die. The veterinarians get a kick-back from pushing this drug from what I understand from a vet tech I ran into at a mall. She said she observed the drug company rewarding vets with Yeti coolers, vacation trips and money, etc. The vets can’t be that unaware of what these drugs are doing to our dogs! Everyone wants to just sweep it under the rug! It’s time for veterinarians to stand up and take up for our dogs! I have found very few that want to agree with me which is shameful!!! As you can see, I am speaking my mind especially since I’ve been dealing with all these health issues going on a year now.

  9. Phillip Ramsey says

    These comments are scary and causing me to have concern about using this
    Is there any studies made about these side effects
    My guys have been with us for all their lives

  10. Lynn Smith says

    took both dogs off trifexis. Caused vomiting and loss of hair in my dogs. trip to vey every month because of this medicine. Took both off and no more problems. My vet said that it was not the cause…. but all stopped when trifexis was stopped.

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