Short answer: NexGard kills fleas and ticks, and NexGard Spectra does that and also prevents heartworm and clears common intestinal worms, but Spectra is sold in Europe and the UK, not in the US.
If you’re in the US and want that broader cover, the product your vet can prescribe is NexGard PLUS, which the FDA approved in July 2023 and which works a little differently.
Maybe a friend in Europe swears by Spectra, or you landed on a page that compares it to NexGard as if both were on the shelf at your vet. Then your vet mentions NexGard PLUS instead, and the names start to blur.
There are really three chews here, from the same company, with the same flea and tick ingredient and different extras. This guide puts them side by side, with what each label covers and what the trials found.
| NexGard | NexGard PLUS | NexGard Spectra | |
|---|---|---|---|
| Where it’s sold | US, plus the UK and EU | US | EU, UK and elsewhere, not the US |
| Active ingredients | Afoxolaner | Afoxolaner, moxidectin, pyrantel | Afoxolaner, milbemycin oxime |
| Fleas | Yes, one month | Yes, one month | Yes, 5 weeks |
| Ticks | Six US species | Six US species | Five European species, 4 weeks |
| Lyme prevention by killing ticks | Yes | Yes (added April 2025) | Not on the UK label |
| Heartworm prevention | No | Yes | Yes |
| Roundworms and hookworms | No | Yes | Yes |
| Whipworm | No | No | Yes |
| Lungworm and eyeworm | No | No | Yes |
| Mange, demodex, ear mites | Not on the US label | Not on the US label | Yes |
| Tapeworm | No | No | No (only lowers the risk by killing fleas) |
| Youngest and smallest dog | 8 weeks and 4 lb | 8 weeks and 4 lb | Vet’s call under 8 weeks or 1.35 kg (3 lb) |
| Prescription | Yes | Yes, after a negative heartworm test | Yes |
From the US labels on DailyMed, the FDA approval summary for NexGard PLUS and the UK product characteristics for NexGard Spectra, checked 19 October 2026. NexGard sold in the UK and EU carries extra mite claims that the US label doesn’t.
Why you won’t find Spectra at a US vet
NexGard Spectra has held a European marketing authorisation since 15 January 2015, and it’s a prescription medicine in the EU and in Great Britain.
In the US, I couldn’t find any FDA approval for the afoxolaner and milbemycin oxime combination, and Boehringer Ingelheim’s US NexGard site lists only NexGard, NexGard PLUS and NexGard COMBO, a topical for cats.
So for a US dog the real choice is between NexGard and NexGard PLUS, and Spectra matters mainly if you live in Europe or you’re moving there with your dog.
NexGard: fleas and ticks, nothing else
NexGard is a monthly beef-flavored chew with one active ingredient, afoxolaner, a drug from the isoxazoline family that kills fleas and ticks by acting on their nervous systems.
It comes in four strengths, 11.3, 28.3, 68 and 136 mg, for dogs from 4 to 10 lb up to 60.1 to 121 lb, and it’s labeled for dogs from 8 weeks old and 4 lb.
According to the US label, it began killing fleas four hours after the first dose and was more than 99% effective at eight hours. Fleas that arrived later were all dead within 24 hours for 35 days.
The faster 12-hour kill does fade toward the end of the month: on Day 28, NexGard was 81.1% effective 12 hours after new fleas landed, which is worth knowing if your dog picks up fleas often.
It treats and controls six US tick species: black-legged, American dog, lone star, Gulf Coast, brown dog and longhorned ticks. The Gulf Coast tick was added in March 2026.
NexGard is also labeled to prevent Lyme infections as a direct result of killing black-legged ticks, and it has no worm, heartworm or mange claims on its US label.
90-day US field study
Study: 615 dogs in 333 households, 415 of them on NexGard, compared with an oral flea treatment
Result: Flea counts fell 98.0%, 99.7% and 99.9% at Days 30, 60 and 90, with no serious adverse reactions
Lyme transmission study
Study: 20 dogs exposed to wild ticks, 67% of them carrying Lyme bacteria, 28 days after treatment
Result: None of the 10 treated dogs became infected, against 9 of the 10 untreated dogs
From the US NexGard label and a 2016 study in Comparative Immunology, Microbiology and Infectious Diseases, both linked in the references.
One nuance: the label says NexGard kills fleas before they can lay eggs, yet in the lab, dogs given fleas the day before treatment still produced a few eggs in the first 12 to 24 hours.
In February 2026 the FDA also issued an emergency use authorization for NexGard to treat New World screwworm infestations in dogs. That is an emergency use, not an approved indication.
NexGard PLUS: the US answer to Spectra
NexGard PLUS keeps afoxolaner and adds two dewormers, moxidectin and pyrantel, so the same monthly chew also prevents heartworm disease and treats and controls roundworms and hookworms.
The FDA approved it on 19 July 2023, it comes in five strengths for dogs from 4 to 132 lb, and the same 8-week, 4 lb minimum applies.
Before your vet prescribes it, your dog needs a negative heartworm test, as Boehringer Ingelheim notes, because NexGard PLUS prevents heartworm but doesn’t kill adult heartworms already in the dog.
For heartworm prevention, the label says to keep giving it monthly for at least six months after the last exposure to mosquitoes. It has no whipworm, tapeworm or lungworm claim.
Two indications arrived after launch: Lyme prevention by killing black-legged ticks in April 2025, and the Gulf Coast tick in January 2026, where the label gives at least 92% effectiveness, a little below the 97% for NexGard alone.
US heartworm field study
Study: 244 dogs at six clinics in heartworm-endemic areas, given monthly doses over 330 days, 120 of them on NexGard PLUS
Result: None of the 120 NexGard PLUS dogs tested positive for adult heartworms, so effectiveness was 100%
Two lab heartworm studies
Study: Dogs infected with heartworm larvae, then given six monthly doses, 10 treated and 10 untreated in each study
Result: 100% in both studies, with no worms found in any treated dog
From the FDA’s approval summary for NexGard PLUS, checked 19 October 2026.
Resistant heartworm
Two lab studies tested NexGard PLUS against heartworm strains that resist the usual preventives, both alongside Simparica Trio, and their results depend partly on who paid for them.
In a 2024 study funded by Boehringer Ingelheim, NexGard PLUS was 99.5% effective and Simparica Trio 99.8%, with no significant difference. In a 2026 study funded by Zoetis, which makes Simparica Trio, the figures were 98.1% and 99.5%, and 6 of 8 NexGard PLUS dogs had worms against 2 of 8.
Our guide to NexGard PLUS vs Simparica Trio goes further into that comparison.
NexGard Spectra: what the European label covers
Spectra pairs afoxolaner with milbemycin oxime, a dewormer that also prevents heartworm, and it comes in five strengths for dogs from 1.35 to 60 kg, roughly 3 to 132 lb.
On its UK label, it kills fleas for five weeks and ticks for four, treats roundworms, hookworms and whipworm, and prevents heartworm, the lungworm Angiostrongylus vasorum and the eyeworm Thelazia callipaeda.
It also treats demodicosis, which is mange caused by Demodex mites, as well as sarcoptic mange and ear mites, and it only lowers the risk of flea tapeworm by killing fleas, because it has no tapeworm ingredient.
The label is careful about when to use it: only when a dog needs protection against fleas, ticks or mites and against at least one internal parasite at the same time. Otherwise a narrower product is the better choice.
For heartworm, the European schedule is monthly during the mosquito season, continuing until one month after the last exposure, which is much shorter than the six months the US label sets for NexGard PLUS.
Intestinal worms, 10 European countries
Study: 408 dogs, 207 of them on Spectra, compared with a milbemycin and praziquantel dewormer
Result: 99.7% against roundworms, 97.2% against hookworms and 99.7% against whipworm, judged by egg counts
Lungworm prevention
Study: 20 beagles given four monthly doses while exposed to Angiostrongylus vasorum
Result: 94.9% fewer worms and 99.9% less larval shedding than untreated dogs
Demodex mange, NexGard and Spectra
Study: 48 dogs with generalized demodicosis at referral centers in France, Italy and Poland, three monthly doses, no untreated group
Result: Across the study, mite counts fell 87.6%, 96.5% and 98.1% at Days 28, 56 and 84
Sarcoptic mange
Study: 65 dogs in Portugal and Germany, two monthly doses of NexGard or Spectra
Result: Mites fell 99.6% after one month and 100% after two with Spectra, and 98.9% and 99.7% with NexGard
From studies in Parasitology Research, Parasites & Vectors and Parasite, linked in the references. I couldn’t read the European assessment of Spectra’s heartworm studies, so its figures aren’t included here.
Safety: what the labels actually warn about
All three chews contain an isoxazoline, and the US label carries a class warning: these drugs have been linked to tremors, ataxia, which means wobbly, uncoordinated movement, and seizures.
Seizures have been reported even in dogs with no history of them, so the label asks for caution in dogs with seizures or other neurologic problems, and that’s worth raising with your vet before the first dose.
The FDA put out an alert about isoxazolines in September 2018, naming NexGard alongside Bravecto, Credelio, Simparica and Revolution Plus, while saying these products remain safe and effective for most animals.
In the US field study, vomiting was the most common side effect, in 4.1% of NexGard dogs against 12.5% on the comparison product, followed by dry, flaky skin and diarrhea at 3.1% each, lethargy at 1.7% and poor appetite at 1.2%.
In the NexGard PLUS heartworm study, which followed 134 treated dogs, diarrhea showed up in 6.7%, vomiting in 4.5%, and lethargy and itching in 2.2% each.
Pregnant or nursing dogs
The US labels say safe use in breeding, pregnant or lactating dogs hasn’t been evaluated, while the UK Spectra label says it can be used in pregnant and lactating dogs.
Collies and related breeds
The Spectra label asks for the dose to be strictly observed in collies, because of milbemycin. A 2022 study in 30 collies found no significant reactions at about four times the top dose.
Small puppies
The US products start at 8 weeks and 4 lb. Under 8 weeks or 1.35 kg, the UK Spectra label leaves it to the vet’s judgement.
Which one fits your dog
If your vet already has your dog on a separate heartworm preventive, or you only need fleas and ticks handled, plain NexGard covers that and nothing more.
If you’d like one monthly chew for fleas, ticks, heartworm, roundworms and hookworms in the US, NexGard PLUS is the option, after a negative heartworm test, and it isn’t the only combination product your vet may suggest.
If you live in Europe or the UK, or you’re moving there, Spectra is the broader choice, especially where lungworm or mange is a concern, and a local vet will need to prescribe it.
Moving between the two continents? Keep the heartworm schedules in mind, six months after the season on NexGard PLUS and one month on Spectra, and bring your dog’s records so the new vet can decide.
Other names you’ll see in the same aisle
- Simparica began killing fleas three hours after dosing, according to its label, and Simparica vs Simparica Trio explains the difference between the two.
- Bravecto chews cover fleas and most ticks for 12 weeks, but the lone star tick for 8, and they’re labeled for dogs from 6 months and 4.4 lb.
- Capstar is a one-off flea killer that begins working within 30 minutes and was more than 90% effective within four hours, so it doesn’t protect your dog for the month.
- Revolution is a monthly topical that prevents heartworm and treats fleas, ear mites, sarcoptic mange and American dog ticks, for dogs from 6 weeks old.
- Frontline Plus is a topical that kills fleas, ticks and chewing lice and lasts 30 days.
- Seresto is a collar that lasts eight months, and our guide to flea and tick collars compares it with others.
Questions people ask
Is NexGard Spectra available in the US?
No. NexGard Spectra is authorised in the EU and the UK, but I found no FDA approval for it, and Boehringer Ingelheim’s US site lists only NexGard, NexGard PLUS and NexGard COMBO for cats. The US product with heartworm and worm protection is NexGard PLUS.
What is the difference between NexGard and NexGard Spectra?
NexGard contains only afoxolaner, which kills fleas and ticks. NexGard Spectra adds milbemycin oxime, which prevents heartworm and treats roundworms, hookworms and whipworm, and its European label also covers lungworm, eyeworm and mange.
Is NexGard PLUS the same as NexGard Spectra?
No. Both add heartworm prevention to afoxolaner, but NexGard PLUS uses moxidectin and pyrantel while Spectra uses milbemycin oxime. NexGard PLUS has no whipworm, lungworm or mange claim on its US label.
Is NexGard safe for puppies?
In the US, NexGard and NexGard PLUS are labeled for puppies from 8 weeks old and 4 lb. Like every drug in its class, NexGard carries a warning about tremors, wobbliness and seizures, so tell your vet about any neurologic history.
Can NexGard cause seizures?
Rarely. The label warns that isoxazoline drugs, the class NexGard belongs to, have been linked to tremors, ataxia and seizures, even in dogs with no seizure history. The FDA alerted owners in 2018 but said these products remain safe and effective for most animals.
Do I need a prescription for NexGard?
Yes. NexGard and NexGard PLUS are prescription-only in the US, and NexGard PLUS also needs a negative heartworm test first. NexGard Spectra is prescription-only in the EU and UK.
Does NexGard Spectra treat tapeworms?
No. It has no tapeworm ingredient. Its European label only says it lowers the risk of the flea tapeworm for 30 days by killing the fleas that carry it.
References
US Food and Drug Administration / DailyMed. NexGard (afoxolaner) chewables, US label (US indications, doses, flea and tick figures, field study and safety warnings).
US Food and Drug Administration / DailyMed. NexGard PLUS chewables, US label (heartworm and worm indications, Gulf Coast tick figure and adverse reactions).
US Food and Drug Administration. Freedom of Information summary, NADA 141-554 (NexGard PLUS) (approval date and heartworm studies).
Veterinary Medicines Directorate. NexGard Spectra summary of product characteristics (European indications, schedules and safety wording).
European Commission, Union Product Database. NexGard Spectra product record (EU authorisation date and strengths).
US Food and Drug Administration. Animal drug safety communication on isoxazoline products (the 2018 neurologic adverse event alert).
Parasites & Vectors (2016). PubMed abstract: NexGard Spectra and Angiostrongylus vasorum (lungworm prevention trial).
Parasites & Vectors (2018). PubMed abstract: Afoxolaner and afoxolaner plus milbemycin oxime in generalised demodicosis (demodex field trial).
Parasite (2018). PubMed abstract: NexGard and NexGard Spectra for sarcoptic mange (sarcoptic mange field trial).
Parasitology Research (2017). PubMed abstract: NexGard Spectra against gastrointestinal nematodes in ten European countries (intestinal worm field study).
Comparative Immunology, Microbiology and Infectious Diseases (2016). PubMed abstract: Afoxolaner and Lyme disease transmission (Lyme prevention trial).
Parasites & Vectors (2024). PubMed abstract: NexGard PLUS and Simparica Trio against the JYD-34 heartworm isolate (resistant heartworm study, Boehringer Ingelheim funded).
Parasites & Vectors (2026). PubMed abstract: NexGard PLUS and Simparica Trio against the ZoeLA heartworm isolate (resistant heartworm study, Zoetis funded).
Parasite (2017). PubMed abstract: NexGard Spectra and Dipylidium caninum (flea tapeworm study).
I rewrote this guide in October 2026. The old version treated NexGard Spectra as a US option, missed NexGard PLUS entirely, left out the seizure warning, said puppies have no bad reactions and mixed dollar and pound prices.
The Nomad Paws is in memory of Woody, a great traveler and, most of all, the best, kindest and wisest friend I have ever had.
This guide is research, not a hands-on test: the figures come from the US labels, the FDA and UK regulators and peer-reviewed studies, all read on 19 October 2026. These are prescription medicines, so it isn’t veterinary advice, and the right choice for your dog is one to make with your vet. Here is how I make my guides.
