Yes, NexGard is a prescription-only medication in the United States. Its FDA label classifies it as a “Prescription Animal Drug” and carries the standard federal notice: this drug is restricted to use by or on the order of a licensed veterinarian. You cannot legally buy NexGard without a valid prescription from a vet.
Why NexGard Requires a Prescription
NexGard’s active ingredient, afoxolaner, belongs to a drug class called isoxazolines. The FDA has flagged this entire class for potential neurologic side effects, including muscle tremors, loss of coordination, and seizures. These reactions can occur even in dogs with no prior history of seizures or neurologic problems. That risk profile is a core reason the FDA restricts isoxazolines to prescription-only status: a veterinarian needs to evaluate your dog before deciding if the drug is appropriate.
Dogs that already have a seizure disorder or other neurologic condition may need a different flea and tick product entirely. A vet can also check for drug interactions and confirm the correct dose based on your dog’s exact weight. NexGard comes in four weight-based strengths, and the tablets are not meant to be split. Giving the wrong size can mean your dog gets too little protection or an unnecessarily high dose.
Heartworm Testing Before a Prescription
Many veterinarians will require a heartworm test before writing a prescription for flea and tick prevention, especially if your dog has been off preventives or is a new patient. This isn’t just a formality. According to the American Heartworm Society, giving certain preventives to a dog that already has adult heartworms can trigger rare but potentially severe, even fatal, reactions. The test is a simple blood draw with results typically available within minutes at your vet’s office.
This step applies more directly if you’re getting NexGard Spectra (available outside the U.S.), which adds heartworm and intestinal worm protection through a second active ingredient. Standard NexGard sold in the U.S. covers only fleas and ticks. Either way, most vets treat the visit as an opportunity to confirm your dog is healthy enough for the product.
NexGard vs. NexGard Spectra
Standard NexGard protects against fleas and ticks only. NexGard Spectra adds coverage for heartworm, roundworm, hookworm, whipworm, and lungworm thanks to a second active ingredient. Both products require a prescription. NexGard Spectra is widely available in countries like Australia and parts of Europe but is not currently sold in the U.S. market. If you see it offered online to U.S. buyers, that product is being imported and may not meet FDA packaging or safety standards.
Over-the-Counter Alternatives
Not all flea and tick products require a prescription. Topical treatments like Frontline Plus, which uses a different class of active ingredients (fipronil and methoprene), are available over the counter. These products work through a different mechanism and don’t carry the same neurologic warnings as isoxazolines. The tradeoff is that some dog owners find topical treatments less convenient than a chewable tablet, and effectiveness can vary depending on the flea and tick species in your area.
Other over-the-counter options include flea collars and certain spot-on treatments. These generally use older active ingredients. They’re legal to buy without a vet visit, but they still come with their own safety considerations, particularly for households with cats, since some canine flea products contain ingredients that are toxic to cats.
Avoiding Counterfeit Products Online
Because NexGard requires a prescription, some pet owners turn to discount websites or international sellers that skip the vet step. This is where counterfeit risk enters the picture. The EPA has documented a range of problems with counterfeit pet parasite products sold online, including missing directions in English, no child-resistant packaging, foreign labeling covered by stickers, and missing EPA registration numbers. In some cases the product inside the box doesn’t even match the animal size listed on the packaging.
There’s no single telltale sign that identifies every fake. But any site selling NexGard without asking for prescription verification is a red flag. Legitimate U.S. pharmacies, whether brick-and-mortar or online, will always confirm your vet’s prescription before dispensing the product. Many veterinary clinics also offer the option to buy directly or will work with online pharmacies like Chewy or Petco, where the pharmacy contacts your vet to verify the prescription on your behalf.
What the Vet Visit Looks Like
Getting a NexGard prescription is straightforward. Your vet will weigh your dog, ask about any history of seizures or neurologic issues, and likely run a heartworm test if your dog hasn’t had one recently. If everything checks out, you’ll get a prescription that typically covers 6 to 12 months of doses. Some clinics dispense NexGard directly; others write a prescription you can fill at a pet pharmacy of your choice.
Once prescribed, NexGard is given once a month as a beef-flavored chewable. Most dogs take it willingly as a treat. The minimum requirements for safe use are a dog at least 8 weeks old and weighing at least 4 pounds. For very small puppies under that threshold, a vet would need to weigh the risks and benefits individually before prescribing.