Trifexis vs Comfortis

When it comes to safeguarding our furry friends from pests like fleas and heartworms, the options can be overwhelming. Among the top contenders in the veterinary world are Trifexis and Comfortis. While they might sound similar, there are notable differences that every pet owner should be aware of.

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1. What Are Trifexis and Comfortis?

Trifexis: Trifexis is a monthly chewable tablet designed for dogs. It offers three-in-one protection against fleas, heartworm disease, and other intestinal parasites (like hookworms, roundworms, and whipworms).

Comfortis: Comfortis, on the other hand, is a chewable tablet that strictly offers protection against fleas. It starts killing fleas within 30 minutes of ingestion and has been proven to kill 100% of adult fleas within 4 hours.

2. Active Ingredients

Trifexis: This product combines two key ingredients – spinosad and milbemycin oxime. Spinosad tackles fleas, while milbemycin oxime is responsible for protecting against heartworms and intestinal parasites.

Comfortis: Spinosad is the sole active ingredient in Comfortis, making it a potent flea killer.

3. Benefits & Limitations



  • Comprehensive protection against fleas, heartworms, and several types of intestinal parasites.
  • A once-a-month pill simplifies the protection regime.


  • Does not offer protection against ticks.
  • Some dogs may experience side effects.



  • Specifically designed for robust flea control.
  • Fast-acting formula ensures fleas are killed rapidly.


  • Solely targets fleas, offering no protection against other pests.
  • Not suitable for heartworm prevention.

4. Which One Should I Choose?

The decision between Trifexis and Comfortis largely depends on your dog’s needs and your geographical location:

  • For Comprehensive Protection: If you reside in an area prone to heartworms and intestinal parasites, Trifexis might be a better fit.
  • Strictly for Fleas: If fleas are your primary concern and you already have a separate heartworm preventive regimen in place, Comfortis is a solid choice.

5. Side Effects and Precautions

While both medications are generally safe, they may have potential side effects:

Trifexis: Vomiting, itching, lethargy, and skin redness. Comfortis: Vomiting, loss of appetite, and lethargy.

Always consult your veterinarian before starting any new medication, and be sure to observe your dog for any adverse reactions.

FAQs: Trifexis vs. Comfortis

Q1. Can I give my cat Trifexis or Comfortis?

Answer: Comfortis has been approved for use in cats, but it’s crucial to use the feline-specific dosage. Trifexis, however, is formulated specifically for dogs. Always consult with your veterinarian before administering any medication to your pets.

Q2. How quickly do these medications start working?

Answer: Comfortis starts killing fleas within 30 minutes of ingestion, eliminating 100% of adult fleas within 4 hours. Trifexis also begins killing fleas within 30 minutes, offering a month-long protection against further infestations.

Q3. My dog is on a heartworm medication already. Can I use Comfortis?

Answer: Yes, Comfortis is a flea-specific medication and can be combined with separate heartworm preventatives. However, it’s essential to consult your veterinarian to ensure there are no potential drug interactions.

Q4. Are there age restrictions for using Trifexis and Comfortis?

Answer: Both medications are typically recommended for dogs 8 weeks of age and older. It’s crucial to ensure the correct dosage based on weight and age, and always consult with a vet for the best guidance.

Q5. How do environmental factors affect the efficacy of these treatments?

Answer: While both treatments are effective regardless of environmental conditions, areas with higher flea infestations may require additional environmental control measures, such as regular cleaning and treating the household, to ensure total eradication.

Q6. Are there any known drug interactions with Trifexis or Comfortis?

Answer: Some drug interactions can occur. For instance, giving Comfortis along with high doses of ivermectin can lead to increased risk of side effects. Always provide your vet with a list of all medications and supplements your pet is taking.

Q7. Can I give Trifexis or Comfortis to a pregnant or lactating dog?

Answer: The safety of these medications in pregnant or lactating dogs has not been conclusively established. It’s essential to discuss this with your veterinarian to determine the best course of action.

Q8. What should I do if I miss a dose?

Answer: If you miss a dose, administer the medication as soon as you remember and adjust the subsequent dosing schedule accordingly. It’s crucial to maintain consistent protection, so ensure that doses are not missed frequently.

Q9. How should I store these medications?

Answer: Both Trifexis and Comfortis should be stored at room temperature in their original packaging, away from moisture and direct sunlight. Ensure they are kept out of reach of children and pets.

Q10. What if I see fleas on my dog after administering the medication?

Answer: No flea treatment can prevent fleas from jumping onto the dog. However, with these medications, fleas will be killed within hours. Continuous environmental control measures can further reduce the flea population in your home and surroundings.

Q11. Why might my dog still itch even after flea treatment?

Answer: While these medications kill fleas effectively, dogs might still itch due to the residual flea saliva from bites before the treatment. Other causes, like allergies, dermatitis, or other pests, might also be culprits. Consulting a vet can pinpoint the exact cause.

Q12. Are there any specific breeds that react adversely to Trifexis or Comfortis?

Answer: Some breeds with hereditary sensitivities, like collies, may react to certain drug ingredients. While these medications are generally safe, always discuss breed-specific concerns with a veterinarian.

Q13. Can these medications be used during all seasons?

Answer: Yes, both Trifexis and Comfortis offer protection irrespective of the season. However, in areas where fleas are prevalent year-round, consistent monthly dosing is crucial.

Q14. If my pet vomits after taking the medication, should I give another dose?

Answer: If vomiting occurs within an hour of administration, it’s advisable to give another full dose. However, recurrent vomiting can indicate an adverse reaction, so consultation with a veterinarian is essential.

Q15. How do these oral medications compare with topical flea treatments?

Answer: Oral treatments offer faster flea eradication, aren’t washed off during baths, and there’s no risk of chemical contact with human skin. Topicals, however, can sometimes offer broader pest protection, including ticks.

Q16. What precautions should I take when transitioning from one flea medication to another?

Answer: Ensure there’s no overlap between doses to prevent overdosing. A vet can provide guidance on transition timelines and highlight any potential interactions or side effects.

Q17. Can Trifexis or Comfortis cause discoloration of my dog’s coat?

Answer: There’s no documented evidence that these medications cause coat discoloration. If changes in coat appearance are observed, they’re likely due to other factors.

Q18. Are there any natural remedies or preventatives I can use alongside these medications?

Answer: Some pet owners use natural remedies like diatomaceous earth, but their efficacy varies. While they might deter pests, they often don’t eliminate them. Always ensure any natural remedy doesn’t interfere with the efficacy or safety of prescribed treatments.

Q19. Can these medications affect my dog’s behavior?

Answer: While rare, some dogs might exhibit behavioral changes like lethargy or agitation due to medications. Monitoring your pet after a new medication introduction is always a good practice, and any concerns should be addressed with a veterinarian.

Q20. Are there any discounts or programs to make these treatments more affordable?

Answer: Some veterinary clinics or manufacturers offer loyalty programs or discounts for bulk purchases. Checking with local vets or online pharmacies can help identify potential savings.

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