Trifexis vs Comfortis

It can be hard to know what’s best for your dog. Take parasite control as an example. There’s so much choice that it becomes baffling.

The packaging all looks great with pictures of happy, parasite-free pets, but the truth is that it’s what’s inside the box that counts.

Take Trifexis vs Comfortis.

You want an effective product that kills fleas. Both products claim to do this.

Yet one product is slightly more expensive but kills other parasites as well. Should you pay the extra and get a wider cover?

The answer isn’t always straightforward.

But this is why we’ve created this article…so all will become clear.

Which is Best: Comfortis or Trifexis?

The first thing to say is they are both great products.

This isn’t a matter of one being better than the other at what they do, but rather that they work against a different range of parasites.

OK, so what does Comfortis vs Trifexis have in common?

The simple and most important answer is that they both kill fleas.

Indeed, both of them contain the same ingredient, Spinosad, to do this.

Other similarities are that they both come in tablet form, are rapid-acting, and carry on working for 30 days.

Great! Easy peasy. Trifexis is more expensive, so I’ll choose the more economic option of Comfortis.

Not so fast!

Along with spending those extra dollars, you get extra benefits, namely getting rid of a group of internal parasites.

This is because Trifexis contains an added ingredient, milbemycin.

Now milbemycin is a member of the avermectin family (the big daddy of which is Ivermectin).

It is effective at killing several common intestinal parasites plus heartworm…so you see those extra dollars could be money well spent.

By paying more for one product (Trifexis) you may be able to skip buying a specific heartworm product…and that means saving money!

How to Decide between Trifexis vs Comfortis for Dogs

Let’s approach this logically.

Start at the beginning by thinking about what your dog’s needs are.

Is he already on a heartworm preventative?

Do you give him regular worming tablets?

Are you only worried about fleas?

If you have the other bases are already covered and your only concern is fleas, then it’s a no brainer…go for Comfortis.

However, to be sure, do the math to check how much you are paying out for these other treatments and if Trifexis would work out more economic.

If you get the same level of cover (so the types of parasites taken out are the same) then go with the cheaper option.

But do be careful, because it’s easy to trip up.

For example, Trifexis doesn’t get rid of tapeworm (more of this in the detailed breakdown of what Trifexis treats) whereas other broad-spectrum worms such as Drontal or Milbemax do.

This means when you dig beneath the surface you aren’t comparing like with like.

At the end of the day, it’s about what you need to do to keep your dog safe and healthy.

Work this out first and then tick the boxes on products that keep him that way.

To help you decide let’s do a quick comparison of Comfortis vs Trifexis:


  • Made by Lily
  • Active Ingredients: Spinosad


  • Made by Elanco
  • Active Ingredients: Spinosad + Milbemycin

Their spectrum of activity is:

Comfortis Effective at Killing

  • Fleas

Trifexis Effective at Killing

  • Fleas
  • Hookworm
  • Whipworm
  • Roundworm
  • Prevention of heartworm

Why Choose Comfortis?

Your dog picks up fleas from the neighbor’s hound.

You want rid of the fleas.


Then Comfortis is the treatment for you.

Give a simple tablet and half an hour later any fleas on the dog start to die and fall off.

The news gets better because unlike earlier generations of kill ‘em quick flea products, this one carries on working for more than 24 hours, it works for 30 days. Wowza!

It is that simple to get rid of fleas.

Or is it?

The answer is ‘yes’ and ‘no’.

Comfortis (and Trifexis for that matter) kills the fleas on the dog, but not those in the environment.

Since fleas only hitch a ride on the dog to feed, and then hop off to lay their eggs and party in the soft furnishings, then you may still get bitten.

If your dog only has a few fleas, then fill your boots, Comfortis will do the job.

But be aware of a heavy flea infestation or when you have lots of pets (who can potentially harbor fleas) then you need to up the ante.

An all-out assault on fleas means treating all the pets in the house against fleas.

This prevents those pesky parasites from hanging out elsewhere whilst you treat the dog, only to return when you stop.

It also means using an insecticide for home use to zap the fleas and larvae living in the carpet, sofa, bed and ….well you get the idea.

By killing the next generation in the egg and using Comfortis to kill the adults then you well and truly hit the ground running when it comes to flea annihilation.

Is there anything else you should know about Comfortis?

Comfortis is a palatable tablet that your dog will chow down like a treat.

It works best when given with or after food, as this helps its absorption from the gut.

It is available in a wide range of weight ranges to suit every dog; however, it shouldn’t be given to dogs weighing less than 3.3 lbs.

When deciding Comfortis vs Trifexis the lower weight it’s safe to administer to, may make a difference to owners of small dogs.

Trifexis also contains milbemycin and this places additional limits on the weight range, and it can only be given to dogs over 8.5 lbs. (as compared to 3.3 lbs. for Comfortis)

The active ingredient, spinosad, works by over-exciting the flea’s nervous system which leads to flea death.

Serious side effects for the dog are unusual and tend to happen only with overdose.

However, vomiting after giving the tablet is not uncommon.

If the dog is sick within 60 minutes of giving a Comfortis tablet, it’s best to go right ahead and give another dose.

Also, as with so many pharmaceuticals, Comfortis hasn’t been fully tested in pregnant or lactating females.

It’s not licensed for use in pregnant dogs or those nursing pups so play it safe and don’t use it if you have a mother dog.

You don’t want to accidentally harm those pups!

Oh yes, when weighing up Trifexis vs Comfortis you might want to consider if your dog is overly sensitive to avermectins.

This can either be breed-related (Collie breeds can be more sensitive than others to this family of drugs) or because your dog is already on a medication containing an avermectin and would risk overdose if given some more in a different form (such as Heartgard, Iverhart Plus, and Ivomec).

Whereas Trifexis contains milbemycin, Comfortis does not, so the latter is the safer option if this is a concern for you.

You can get Comfortis either directly from your vet or via vet’s prescription redeemed at a reputable pharmacy (online or otherwise).

Why Choose Trifexis?

Turning things around, let’s look at the benefits of Trifexis vs Comfortis for dogs.

OK, so we know Comfortis and Trifexis both contain spinosad and are great options for killing fleas quickly and for several weeks.

Also, Trifexis contains milbemycin, which is effective against several major internal parasites.

This makes Trifexis a great option to cover routine worming as well as flea control.

With Trifexis on board, you don’t have to worry about your dog and roundworms (with the possible risk of human infection), whipworms, and hookworms.

Also, Trifexis is a heartworm preventative.

However, if your dog has been unprotected for a while then your vet needs to screen for possible heartworm infection.

Trifexis may well be used to kill immature forms of heartworm, but then the big guns of heartworm adulticides will need to be introduced to purge the active infection.

Unfortunately, nothing about heartworm is straightforward or pleasant, so by far and away, the dog’s best option is the regular use of a preventative such as Trifexis.

As already mentioned the inclusion of milbemycin means Trifexis is only suitable for dogs weighing more than 8.5 lbs.

Like Comfortis, it hasn’t been safety tested in pregnant or nursing dogs and therefore should not be used.

Indeed, pups should be older than 14 weeks before starting Trifexis.

The manufacturer advises that if in doubt between two sizes, it’s best to slightly under dose than overdose, so go for the lower weight range.

Milbemycin works by making the parasites’ outer integument (their ‘skin’) which allows chloride ions to flood in, causing paralysis and parasite death.

However, be aware that great as milbemycin is, it doesn’t kill tapeworms.

Therefore if your dog hunts and eats vermin or has a heavy flea infestation (fleas carry tapeworm eggs) you need to speak to your vet about a product that contains praziquantel or pyrantel, to kill tapeworms.

Trifexis is also a prescription product meaning you need to get it from a vet clinic or use a vet’s prescription at a pharmacy.

Comfortis vs Trifexis

Both Trifexis and Comfortis are tablets.

Many pet parents have a personal preference for how they medicate their pets.

In the past ten years or so, spot-on treatments have ruled the roost because they were easier than the then alternative – a spray.

However, the next generations of parasite products are coming through in tablet form, and beginning to take up were spot-on left off.

What so great about tablets?

These aren’t horse pills that taste like chalk and are impossible to give.

Both Comfortis and Trifexis are tasty treat sized pills that dogs happily accept as a reward.

This makes dosing them a whole lot easier.

Besides, once the tablet is onboard your dog remains huggable.

This is contrasted with a spot-on where you need to plan and apply before bedtime so you can avoid touching their fur while the treatment dries.

Of course with a tablet as an inside load, there’s no need to worry about washing the product off at bath time or restricting your dog’s love of swimming.

Oh yes, and another thing about spot-on is that some can damage the soft furnishings (especially leather sofas) if the dog rubs against them.

To Summarize: Why Choose Comfortis or Trifexis for Dogs?

The things that Comfortis vs Trifexis have in common (apart from being effective at what they do) are:

  • Both are a tasty tablet
  • Both kill fleas present on the dog within 30 minutes of feeding
  • Both carry on working for 30 days

Another factor they both have in common is they only kill fleas that are actually on the pet.

Thus, although both will bring a flea infestation under control, you also need to use environmental control to get rid of flea eggs and larvae.

If flea control is your sole concern, and especially if your preference is for a tablet, then look no further than Comfortis.

However, if you want to nail many potent unpleasant parasites, including roundworms (essential if you have children) or heartworm, then Trifexis is a better choice.

Both products require a prescription, so simply ask your vet to write one for your preferred product and then you and your dog are good to go and enjoy a parasite-free party in the park. Read our comprehensive guide on Dog Medication here and for those interested, a detailed article covering how long fleas live for without food. 

Dr Sarah Robinson attended veterinary school at Oklahoma State University receiving a D.V.M. in 2008. Sarah’s longtime interest is to help people to better communicate with their pet companions, and in doing so, to help them to strengthen their relationships with their dogs and cats. Sarah has published numerous articles on canine feeding in pet related magazines, veterinary journals and leading natural health web sites.

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