Comfortis vs NexGard: what's the difference?
How Comfortis and NexGard compare: what each is for, how it works, side effects and cost, side by side.
Last updated: October 2026 · 2 sources · see sources
Side by side
| Comfortis | NexGard | |
|---|---|---|
| Generic name | Spinosad | Afoxolaner |
| Brand names | Comfortis, Trifexis | NexGard, NexGard Plus, NexGard Spectra |
| For | Dogs and cats | Dogs |
| Prescription | Prescription | Prescription |
| Used for | A monthly chewable that kills fleas in dogs and cats. [1] | A monthly chew that kills fleas and ticks in dogs and helps prevent Lyme disease. [2] |
| How it works | It overstimulates the flea's nervous system. [1] | It spreads through the dog's body, and fleas and ticks die after biting. [2] |
| Common side effects | Vomiting, low appetite, diarrhea and drooling. [1] | Very few in most dogs. Vomiting and diarrhea can happen. [2] |
| Use with care | Use caution in pets with seizures and pets taking ivermectin at high doses. [1] | An isoxazoline: the FDA has warned of possible tremors, wobbliness and seizures. Not for puppies under 8 weeks or 4 pounds unless your vet says so. [2] |
| Full guide | Comfortis guide | NexGard guide |
Key differences
- They aren't made for the same animals: Comfortis is for dogs and cats; NexGard is for dogs.
Which one is right for my pet?
That is a call for your vet. They weigh your pet's age, weight, other health problems, other medicines and what you can realistically give at home.
Switching from Comfortis to NexGard is common, but do it only with your vet's plan.
Common questions
What is the difference between Comfortis and NexGard?
Comfortis is a monthly chew that kills fleas only; NexGard covers fleas and ticks in dogs.
Is Comfortis better than NexGard?
Neither is better for every pet. Your vet chooses based on your pet's species, age, health history, other medicines and what you can manage at home.
Can my pet take Comfortis and NexGard together?
Only if your vet says so. Some medicines in the same family should not be combined, and others are often used together. Always check before adding or switching.
Do Comfortis and NexGard need a prescription?
Comfortis: Yes. It needs a prescription from a veterinarian. NexGard: Yes. It needs a prescription from a veterinarian.
Related
This page is general information for planning, not veterinary advice. Talk to your vet about your own pet.