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Simparica vs Comfortis: Key Differences (Vet Answer)

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By Dr. Joanna Woodnutt

Simparica vs Comfortis

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Written by

Dr. Joanna Woodnutt

BVM BVS (Veterinarian)

The information is current and up-to-date in accordance with the latest veterinarian research.

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Simparica and Comfortis are chewable pet parasite treatments. The active ingredients in both products are designed to kill adult fleas quickly and effectively and can be given monthly to your pet to prevent further issues with fleas. Both treatments come in easy-to-give chewable tablets, but they contain slightly different active ingredients – Simparica contains the ingredient sarolaner, while Comfortis contains spinosad. Although both products are very popular with pet parents and veterinarians, there are some key differences between them.

Comfortis is designed to kill adult fleas only, with no effect on any other parasites, whereas Simparica has a broader spectrum of action against ticks and mites as well. So, if you’re looking for broad cover against fleas, ticks, and mites, Simparica is likely to be your product of choice, but if you’re simply looking to get rid of fleas fast and prevent further problems, then Comfortis might be sufficient for your pet.

Both products are for use in dogs, but Comfortis can also be used in cats. Both products require a veterinary prescription and are widely available from your veterinary clinic or online pharmacy. Neither product is known to have any major side effects, and both are known to be safe and effective.

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At a Glance

Simparica vs Comfortis

Let’s look at the key points of each product.

  • Active ingredient – Sarolaner
  • Dogs only
  • Comes in an easy-to-give chewable tablet
  • Designed to be given monthly, but effects last for 35 days
  • Kills adult fleas, ticks, and mites
  • Kills fast with the onset of action from 3 hours after dosing, and kills up to 95% of fleas within 8 hours
  • Safe and effective
  • Can be given to dogs from 6 months old
  • Prescription-only product
  • Active Ingredient – Spinosad
  • Dogs and cats
  • Comes in an easy-to-give chewable tablet
  • Designed to be given monthly
  • Kills adult ticks only
  • Kills fast with the onset of action from 30 minutes after dosing, and kills 100% of fleas in dogs and 98% of fleas in cats within 4 hours
  • Safe and effective
  • Can be given to dogs and cats from 14 weeks old, and weighing over 1.8kg (cats) and 2.2kg (dogs)
  • Prescription-only product

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Overview of Simparica


  • Easy to give in a chewable tablet
  • Kills not only fleas but ticks and mites too
  • It is the only licensed oral product in the UK to treat Demodex canis, Otodectes cynotis, and Sarcoptes scabei
  • It is effective against 99% of UK ticks, and 5 types of tick in the USA, including the Gulf Coast tick
  • In the USA it is FDA approved to block infections causing Lyme’s disease in dogs
  • The effects last for 35 days after dosing, which means if you are late giving your dog his monthly treatment, you are still covered
  • Safe and effective
  • Only available with a prescription from your veterinarian
  • Only kills adult fleas, and does not kill eggs or larvae
  • Takes up to 3 hours to start working after giving to your pet
  • Can only be given to dogs
  • Not suitable for dogs under 6 months of age

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Overview of Comfortis

  • Easy to give in a chewable tablet
  • Can be given to dogs and cats
  • Fast-acting within 30 minutes of giving to your pet
  • Kills 100% of fleas on dogs and 98% of fleas on cats within 4 hours
  • Safe and effective
  • Lasts for one month and can be used monthly to prevent fleas
  • Can be given to dogs and cats from as early as 14 weeks old
  • Only available with a prescription from your veterinarian
  • Only kills adult fleas, and does not kill eggs or larvae
  • Not effective against any other parasites

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What Are the Differences Between Them?

Parasites Treated

Although fleas are the most common parasite to affect our pets, there are other creepy crawlies out there that can affect them too, such as ticks and mites. Both Simparica and Comfortis focus on fleas, but Simparica has some additional benefits by protecting your pet against ticks and mites too. Comfortis only kills fleas. So if you are looking for a broader spectrum of cover for a reasonable price, Simparica may be the best product for your pet.

Simparica is effective against 99% of UK ticks, and 5 species of ticks in the USA (including the Gulf Coast tick). In the USA Simparica is also FDA approved to prevent infections that cause Lyme disease (a disease that can be caught from tick bites). In the UK the license for Simparica also covers Demodex canis, Otodectes cynotis (ear mites), and Sarcoptes scabei (the mite that causes sarcoptic mange).

It’s important to also remember that both products only kill adult fleas, and have no effect on eggs or larvae. Although both are designed to kill fleas fast to minimize the number of eggs laid, it will take a minimum of 3 months of treatments to break the flea cycle and completely eliminate the problem.

removing mite and flea from dog paw
Image Credit: Naurora, Shutterstock

Speed of Treatment

Simparica and Comfortis act quickly to kill fleas, with their onset of action occurring very soon after dosing. If you are tackling a flea problem on your pet, then you will be looking for the fastest-acting product to get on top of things quickly. Comfortis acts faster than Simparica, with the onset of action being within just 30 minutes after treatment. This is compared to 3 hours for Simparica, which is quite a bit slower.

Within 4 hours of giving Comfortis, almost all the fleas will be killed, whereas this takes up to 8 hours after giving Simparica. So, if it’s speed of treatment that you’re after, Comfortis comes out on top here.

Price and Availability

Simparica and Comfortis are both prescription-only products, which means you will need to either purchase them directly through your veterinary clinic or obtain a prescription from them to take elsewhere. Both products are easily available through your vet clinic, but they can also be purchased from licensed online pharmacies.

Both products are at the cheaper end of the spectrum when it comes to the cost of parasite treatments. Simparica does come in slightly cheaper than Comfortis, so if cost is a big factor for you when choosing the best product for your pet, this might be the best choice.

Dosage and Ease of Use

Both Simparica and Comfortis are chewable tablets. This makes them easy to give to your pet and means there are no nasty treatments left on the fur that could wash off or cause irritation if licked. Simparica is liver flavored while Comfortis is beef flavored, so both products are tasty and appealing to your pet!

The dosage of both products is based on your animal’s weight, so you will need to weigh your pet at the veterinary clinic to ensure you get the right size tablet for your dog or cat. The dosing instructions on the packaging are clear, and your veterinarian will be able to guide you on dosing when preparing your prescription.

Both products are given monthly, but Simparica has the added benefit of lasting for 35 days, so if you run a little late giving your pet their monthly treatment, you don’t have to worry as they are still covered for an extra 5 days.

chewable tablets for dogs
Image Credit: Merrimon Crawford, Shutterstock


Pets of any age can get fleas, but not all products on the market are suitable for very young animals. So if your pet is very young, you may be more limited with your choices. Simparica cannot be given to dogs under 6 months of age, but Comfortis can be given from 14 weeks of age. If your pet is younger than this and needs flea treatment, speak to your veterinarian for advice.

Side Effects

Simparica and Comfortis are both very safe for pets, with few known side effects. However, both can cause some mild vomiting or diarrhea. In rare cases you may notice lethargy, scratching, ataxia (wobbling and walking like they are drunk), and convulsions. These side effects are rare, but if you notice any unusual symptoms after giving your pet either product then you should contact your veterinarian straight away.

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What the Users Say

We’ve researched what other pet parents have to say about these products. We’ve done this by reading reviews from users, and by paying attention to forum discussions.

Range of action

As we have already discussed, Simparica has a broader range of action against ticks and mites as well as fleas, and a lot of pet parents seem to prefer the product for this reason. However, both products are well regarded for being affordable and effective flea treatments for dogs or cats.

Ease of use

When it comes to ease of use, pet parents frequently comment on how easy it is to give their pet the chewable tablets, and that they prefer these products compared to spot-ons, which can be messy and irritating to pets. However, a few users do report that they noticed some mild vomiting after giving their pet the treatment, especially after giving Simparica.


Reviews for both products generally state that users notice a reduction in the number of fleas on their pets after giving Simparica or Comfortis, and pet parents seem to be generally very happy with the results they see after giving either Simparica or Comfortis. However, as we have discussed, both products only kill adult fleas and not the eggs or larvae, which is commented on by many users who notice that it can still be difficult to get right on top of a flea problem with these products.


The consensus from pet parents is that both Simparica and Comfortis are highly effective at killing fleas, come at an affordable price, and are easy to give. However, many users prefer the lower price and broader range of action of Simparica.

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Final Thoughts

Simparica and Comfortis are pet flea treatments, particularly known for being easy-to-give, chewable tablets that work to kill fleas quickly and effectively. Simparica is slightly cheaper than Comfortis and is also effective against mites and ticks. However, it cannot be used in pets under 6 months of age. Both products effectively kill adult fleas within just a short time after being given and last for a month. Simparica has a few days of extra protection (up to 35 days) in case you are late giving your pet their next dose. There are pros and cons to both products, and both are popular among pet parents.

Always speak to your veterinarian to discuss the parasite control and treatment protocols for your pet, as they will be able to recommend the best products for your pet, and help you in purchasing the most suitable product.

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