NexGard vs Simparica: What's the Difference?

NexGard vs Simparica: The Core Difference

NexGard (afoxolaner) and Simparica (sarolaner) are both monthly isoxazoline-class chewable flea and tick treatments for dogs. They're different drugs made by different manufacturers, but their mechanism of action is similar: they kill fleas and ticks systemically by acting on the parasite's nervous system. The practical differences are subtle but worth understanding before choosing.

Note: This article compares standard NexGard and standard Simparica. Both products also have expanded versions — NexGard Spectra and Simparica Trio — that add heartworm and intestinal worm coverage. If you want all-in-one protection, see our NexGard Spectra vs Simparica Trio comparison.

Active Ingredients

NexGard contains afoxolaner (made by Boehringer Ingelheim). Simparica contains sarolaner (made by Zoetis). Both are isoxazolines — a drug class that kills external parasites by overstimulating their nervous system, causing paralysis and death.

Side-by-Side Comparison

Which Acts Faster?

Simparica has a meaningfully faster onset. It starts killing fleas within 3 hours and ticks within 8 hours. NexGard starts killing fleas within 8 hours and ticks within 48 hours. For households with active flea infestations where you need rapid relief, Simparica's faster action is a genuine advantage. For a broader look at tick kill speeds across all products, see our tick prevention for dogs guide.

Puppy Age Restriction: An Important Difference

NexGard is approved from 8 weeks of age (minimum 4 lbs). Simparica requires dogs to be at least 6 months old. This is a significant distinction for puppy owners — if your dog is under 6 months, NexGard is the appropriate choice between these two. Simparica Trio (the expanded version) also has the 6-month minimum age restriction.

Tick Coverage

Both NexGard and Simparica protect against 5 tick species: black-legged ticks, American dog ticks, brown dog ticks, lone star ticks, and Gulf Coast ticks. Coverage breadth is essentially equivalent.

Which Is More Widely Used?

NexGard has historically been the market leader for monthly oral flea and tick treatments in the USA, with a longer track record. Simparica is newer but has rapidly gained popularity due to its faster speed of kill. Both are considered safe and effective. To understand how to buy either without a prescription, see how to buy pet medications from Australia.

Price

NexGard and Simparica are comparable in price from Australian retailers. Both are significantly cheaper through Australian sources than from US vets or US-based pharmacies. See why pet medications are cheaper from Australia for a full explanation.

Which Should You Choose?

For puppies under 6 months: choose NexGard — it's approved from 8 weeks, Simparica is not.
For fastest flea relief: choose Simparica — it starts killing fleas within 3 hours.
For broadest parasite coverage: consider Simparica Trio or NexGard Spectra — see our NexGard Spectra vs Simparica Trio comparison for the full breakdown.

Shop NexGard → | Shop Simparica →