NexGard for Dogs

NexGard for Dogs

By Dr Duncan Houston

If you are choosing flea and tick protection for your dog, NexGard is one of the most commonly prescribed options. It is convenient, effective, and easy for many owners to give. But convenience should never be the only reason to choose a parasite product. What matters most is whether it is the right fit for your dog’s age, health status, lifestyle, and risk profile.

For most dogs, NexGard works well and side effects are mild if they happen at all. But there are still important things owners should know, especially around neurological risk, vomiting after dosing, and what to do if your dog has reacted badly to parasite preventives before.

Quick Answer

NexGard is a monthly oral flea and tick chew for dogs that contains afoxolaner. It is highly effective and convenient, and most dogs tolerate it well. The main side effects are mild digestive upset or lethargy, but dogs with a seizure history need extra caution because rare neurological reactions can occur.

What Is NexGard?

NexGard is a prescription monthly chewable parasite preventive for dogs.

Its active ingredient is:
• Afoxolaner

It is used to kill:
• Fleas
• Ticks

It is approved for dogs from:
• 8 weeks of age and older
• At least 4 pounds in body weight

This is a dog product only. It should not be used in cats.

How Does NexGard Work?

Afoxolaner affects the nervous system of fleas and ticks, leading to their death after they bite your dog.

What matters practically:
• It starts working after administration
• It protects for about 30 days
• It is given as a chew, not a topical

For many owners, this is a major advantage because there is:
• No greasy residue
• No concern about bathing washing it off
• No spot-on application issues

Why Do So Many Owners Choose NexGard?

The main reason is simplicity.

It is popular because:
• It is easy to give
• Many dogs take it willingly
• Monthly dosing is straightforward
• It covers both fleas and ticks

Clinical insight:

The best flea and tick product is often the one an owner can actually give consistently. A great product that gets missed regularly is not a great plan in real life.

Is NexGard Safe for Dogs?

For most dogs, yes.

Most dogs tolerate NexGard very well. When side effects happen, they are usually mild and short-lived.

Common side effects may include:
• Vomiting
• Diarrhea
• Reduced appetite
• Lethargy
• Mild skin or coat changes

Decision checkpoint:

If your dog is otherwise bright, eating, and back to normal within a day, mild side effects are usually not serious.

But there is one group where more caution is needed.

Neurological Risk: What Owners Need to Know

This is the most important safety point.

Like other isoxazoline parasite products, NexGard carries a potential risk of neurological side effects, including:
• Tremors
• Ataxia
• Seizures

These reactions are uncommon, but they matter.

Dogs at higher concern include:
• Dogs with a known seizure disorder
• Dogs with previous neurological episodes
• Dogs that have reacted badly to similar products before

Clinical insight:

Most dogs never have a neurological issue with NexGard. But if a dog already has a seizure history, that changes the conversation. In those dogs, parasite control needs a more careful risk-benefit discussion.

What Side Effects Are Most Common?

Mild digestive upset

This is the most common issue.

What it looks like:
• Vomiting
• Soft stool
• Diarrhea
• Mild nausea

This often happens:
• After the first dose
• Within the first day

Mild lethargy

Some dogs are just a bit quieter than normal for a short period.

Reduced appetite

This is usually temporary if it occurs.

What If My Dog Vomits After NexGard?

This is a very common owner question.

If vomiting happens within 2 hours

The dose may not have been fully absorbed, and your veterinarian may recommend redosing.

If vomiting happens after 2 hours

A replacement dose is usually not needed.

Decision checkpoint:

If your dog vomits once but is otherwise normal, that is usually much less concerning than repeated vomiting, lethargy, tremors, or ongoing refusal to eat.

Severity Framework: Mild Reaction vs Concerning Reaction

Mild

• One episode of vomiting
• Mild soft stool
• Slightly reduced appetite
• Still bright and responsive

What it usually means:
Temporary side effect.

What to do:
Monitor, offer water, and keep an eye on appetite and energy.

Moderate

• Repeated vomiting
• Ongoing diarrhea
• Lethargy lasting more than 24 hours
• Refusing food

What it usually means:
Your dog may be reacting more significantly than expected.

What to do:
Contact your veterinarian.

High Risk

• Tremors
• Weakness
• Unsteady walking
• Marked behavioural change

What it usually means:
Possible neurological reaction.

What to do:
Stop further dosing and seek veterinary advice urgently.

Critical

• Seizure
• Collapse
• Severe neurological signs

What it usually means:
Emergency.

What to do:
Seek immediate veterinary care.

Which Dogs Need More Caution?

NexGard may need more thought in:
• Dogs with seizure history
• Dogs with previous isoxazoline reactions
• Pregnant dogs
• Lactating dogs
• Very medically complex dogs on multiple treatments

Pregnancy and nursing safety is not considered well established enough to use casually without veterinary advice.

When Is NexGard a Good Choice?

NexGard is often a strong option when:
• You want a monthly oral product
• Your dog hates topicals
• You need reliable flea and tick control
• Bathing or swimming makes spot-ons impractical
• Compliance has been poor with other products

This is where oral preventives often shine.

When Might It Be a Poor Fit?

It may be a less ideal choice if:
• Your dog has a seizure history
• Your dog previously reacted to an isoxazoline
• You are uncomfortable with oral systemic products
• Your dog needs a different parasite coverage plan

Clinical insight:

No parasite product is “best” for every dog. The right choice depends on the dog in front of you, not just the label or popularity of the product.

What Should You Do Right Now If You Are Starting NexGard?

Before giving it

• Confirm your dog’s current weight
• Make sure the correct size has been prescribed
• Review any previous medication reactions
• Consider your dog’s seizure history honestly

After giving it

• Watch your dog more closely after the first dose
• Monitor appetite, stool, and energy
• Look for any unusual neurological signs

Do not

• Double dose if you forgot a month
• Give dog NexGard products to cats
• Assume a previous bad reaction was coincidence without discussing it with your vet

Time-based guidance:
• Watch most closely over the first 24 hours
• Reassess if signs persist beyond a day
• Treat neurological signs as urgent immediately

Common Mistakes Owners Make

Assuming flea prevention is automatically low-risk

Every medication has pros and cons.

Ignoring seizure history

This is the biggest safety miss I see with isoxazoline products.

Delaying treatment after neurological signs

If tremors or seizures occur, do not wait to “see how it goes.”

Using convenience as the only deciding factor

Convenience matters, but fit matters more.

Forgetting monthly doses

A product only works when it is given consistently.

How Does NexGard Compare to Topicals or Collars?

Advantages of NexGard

• Easy monthly chew
• No greasy skin residue
• No bathing interference
• Good compliance for many owners

Potential downsides

• Systemic oral exposure
• Neurological caution in sensitive dogs
• Not ideal for every patient

Topicals and collars may be better in some dogs, especially where neurological history changes the risk profile.

FAQ

Is NexGard safe for most dogs?

Yes. Most dogs tolerate it very well, but dogs with seizure disorders need more caution.

Can NexGard cause seizures?

Rarely, yes. This is the most important serious precaution to know about.

What if my dog vomits after taking NexGard?

If vomiting happens within 2 hours, ask your vet whether the dose should be replaced. After 2 hours, redosing is usually not needed.

Is NexGard safe for puppies?

It can be used in puppies 8 weeks and older that weigh at least 4 pounds, under veterinary guidance.

Can cats take NexGard chews for dogs?

No. Dog NexGard chews should never be given to cats.

Final Thoughts

NexGard is a very effective and convenient flea and tick preventive for many dogs, and most dogs do well on it. That is why it is used so widely.

But the right way to think about it is not:
“Is this a popular product?”

It is:
“Is this the right parasite product for my individual dog?”

That question matters most in dogs with seizure history, previous medication reactions, or more complex health needs.

If you are unsure whether NexGard is the right option for your dog, or your dog has had side effects from parasite prevention before, ASK A VET™ can help you work through the risks, alternatives, and next steps with more confidence.