Medication Guide • Reviewed by Dr. Tiffany Delacruz, DVM
Simparica for Dogs
Simparica is a prescription monthly chewable that kills fleas and ticks in dogs. Simparica TRIO adds heartworm and intestinal worm protection in the same chewable.
What Simparica is used for in dogs
- Monthly flea prevention
- Tick prevention (including the ticks that carry Lyme disease)
- Heartworm prevention (Simparica TRIO formulation)
- Roundworm and hookworm control (Simparica TRIO)
How it works
Sarolaner blocks parasite nerve receptors (GABA-gated chloride channels), paralyzing and killing fleas and ticks within hours of biting. It does not repel — pests must bite to be killed.
Available formulations
Flavored chewable, monthly
Simparica TRIO (combo) flavored chewable
Side effects to know
Common side effects
- • Mild GI upset
- • Lethargy after the first dose
These usually resolve on their own. If they persist past the first few doses, ask your vet.
Call your vet immediately if you see
- ⚠ Neurologic signs (tremors, ataxia, seizures)
- ⚠ Severe lethargy
- ⚠ Persistent vomiting
Drug interactions
- • Generally low; consult your vet if your dog takes seizure medications
When not to use
- • Dogs under 6 months of age
- • Dogs with a history of seizures (use cautiously)
- • Dogs with documented sensitivity to isoxazolines
Monitoring during treatment
First-time use should be observed for the first 24 hours, especially in small dogs and dogs with neurologic history.
Need a Simparica refill?
RexVet is the first 501(c)(3) non-profit online vet service in the U.S. Talk to a licensed veterinarian by video, get your dogs's Simparica prescription, and have it shipped through RexVetRx — all for $64.99 per visit.
Book a vet visit — $64.99Simparica for Dogs
Frequently asked questions
How fast does Simparica kill fleas?
Simparica starts killing fleas within 3 hours and ticks within 8 hours of administration, with sustained effect for the full month.
Can I give Simparica with food?
Yes — the flavored chewable can be given with or without food. Many dogs take it like a treat.
What's the difference between Simparica and Simparica TRIO?
Simparica covers fleas and ticks. Simparica TRIO adds heartworm prevention and intestinal worm coverage in the same chewable. TRIO requires a current negative heartworm test.
Can RexVet prescribe Simparica?
Yes. After a quick RexVet video visit and (for TRIO) a current heartworm test, we can send Simparica through RexVetRx for monthly delivery.
Is Simparica safe for puppies?
Simparica is approved for dogs 6 months and older. For younger puppies, your vet will recommend an alternative.
Medical review by Dr. Tiffany Delacruz, DVM
Chief Executive Officer & Lead Veterinarian, RexVet. Licensed in Florida, New York, and Virginia.
Last fact-checked: 2026-05-19
Sources
This page is an educational reference and does not replace veterinary advice. Always consult a licensed veterinarian before starting, changing, or stopping medication for your pet.