The label says, word for word:
NexGard® kills adult fleas and is indicated for the treatment and prevention of flea infestations (Ctenocephalides felis), and the treatment and control of Ixodes scapularis (black-legged tick), Dermacentor variabilis (American dog tick), Amblyomma americanum (lone star tick), Rhipicephalus sanguineus (brown dog tick), and Haemaphysalis longicornis (longhorned tick) infestations in dogs and puppies 8 weeks of age…
There are no known contraindications for the use of NexGard®.
Afoxolaner is a member of the isoxazoline class. This class has been associated with neurologic adverse reactions including tremors, ataxia, and seizures.
Seizures have been reported in dogs receiving isoxazoline class drugs, even in dogs without a history of seizures. Use with caution in dogs with a history of seizures or neurologic disorders.
The safe use of NexGard® in breeding, pregnant or lactating dogs has not been evaluated.
Not for use in humans. Keep this and all drugs out of the reach of children. In case of accidental ingestion, contact a physician immediately.
Keep NexGard® in a secure location out of reach of dogs, cats, and other animals to prevent accidental ingestion or overdose.
Every approved medicine has a field study behind it, and the label prints what happened:
In a well-controlled US field study, which included a total of 333 households and 615 treated dogs (415 administered afoxolaner; 200 administered active control), no serious adverse reactions were observed with NexGard®.
Field study table (afoxolaner group): Vomiting (with and without blood) 4.1%; Dry/Flaky Skin 3.1%; Diarrhea (with and without blood) 3.1%; Lethargy 1.7%; Anorexia 1.2%
In a second US field safety and effectiveness study, NexGard® was administered to 130 dogs with fleas. Adverse reactions included pruritus, diarrhea (with or without blood), vomiting, anorexia, and lethargy.
Approved by FDA under NADA 141-406; FOI summary shows 'Date of Approval: September 14, 2013' with sponsor Merial Ltd. (FDA's 2018 alert notes 'Merial has since transferred ownership of Nexgard's approval to Boehringer Ingelheim'). Label also states: 'NexGard® is indicated for the prevention of Borrelia burgdorferi infections as a direct result of killing Ixodes scapularis vector ticks.'
The emergency page sorts the signs by how long you have, and the symptom checker asks what you are seeing. Reactions to a medicine can also be reported to the FDA yourself: how to report a problem.
These answers come from the approved label on DailyMed, read on 2 October 2026. Where the label does not say, the answer says so, and the vet or the pharmacist is the one to ask.
The approved use is quoted at the top of this page. It is a chewable given to dogs and puppies once a month to kill adult fleas and to treat and control the ticks the label names.
The label says that in a laboratory study NexGard began to kill fleas four hours after the first chewable and was more than 99% effective at eight hours. For ticks, the label gives laboratory results at two points. NexGard was more than 93% effective 48 hours after the ticks got onto the dog for the American dog tick, the black-legged tick and the brown dog tick. It was at least 97% effective at 72 hours for the lone star tick, the longhorned tick and the Gulf Coast tick.
It is given by mouth once a month, with or without food. Make sure your dog eats the whole dose and watch for a few minutes afterwards. If you think part of the dose was lost, or your dog vomits within two hours of it, the label says to give another full dose. Treatment can start at any time of year, and where fleas are common all year round the label says to give it every month of the year without a break. It also says that all the animals in the household should be treated with an approved flea control product.
The label says: "If a dose is missed, administer NexGard and resume a monthly dosing schedule." In plain words, give the chewable and carry on once a month.
The studies and the warnings are quoted above. The label has no line telling owners when to call the vet. It does say that drugs of this class have been linked to tremors, unsteady walking and seizures, and that seizures have been reported even in dogs with no history of them. If you see any of these, or your dog seems unwell after a dose, call the vet. If a person swallows a chewable, the label says to contact a physician immediately.
Store it at or below 86°F. The label allows short spells up to 104°F. Keep it out of the reach of children. The label also says to keep it in a safe place out of reach of dogs, cats and other animals, to prevent accidental swallowing or an overdose.
The FDA says the best way to get rid of most unused or expired medicines is a take-back option: a drug take-back location, which can be at a pharmacy or a police station, or a prepaid mail-back envelope. If you cannot use one, the FDA says a medicine that is not on its flush list can go in the trash at home. Its steps are to mix the medicine with something unappealing such as dirt, cat litter or used coffee grounds, without crushing it, and to seal the mixture in a plastic bag before throwing it away. Flushing is only for medicines on that list, such as opioids. Do not give leftovers to another pet.
Write the dose, the times and the stop date here, then print this page for the fridge.
Dose and times: _____________________________________________
Stop date: _____________________________________________