Comfortis vs. Capstar: 2024 Comparison and Key Differences

Comfortis and Capstar are popular flea treatments for dogs and cats. They are two of the many flea treatments available for pets. Because pets are important to their owners, choosing the right flea treatments is essential. You want to make sure you are giving your beloved pet the best medicine.

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Fleas love dogs and cats. The little insects dig into fur, imbibe your pet’s blood, then excrete tiny flakes on your pet’s skin. Eventually, they mate, lay eggs, and make more fleas. When cats and dogs have fleas, they can’t stop scratching at them. Pets can develop rashes, lose hair, and develop an offensive smell.

Flea medication can work in two ways. They help prevent fleas from invading your pet’s skin and fur, and they can kill them if they already have. Some work in the short term, immediately killing adult fleas. Others work for a month or several months. Medication is delivered in a few different ways.

Some flea medications need the owners to apply it topically. Others require dogs and cats to ingest it as a chew or a pill.

The FDA approved Comfortis as a veterinarian-prescribed medication that kills and prevents flea infestations in cats and dogs. Capstar is also FDA approved, but works to kill adult fleas in cats and dogs; it does not prevent fleas from laying eggs.

What to look for in a good flea treatment

When you begin your search for the best flea treatment for your pet, you must consider your pet’s lifestyle. Pets that spend time outside are more likely to get fleas. The breed, age, and size of your pet also affects the medication you can use. Where you live also affects the effectiveness of the flea medication that you choose for your pet.

Before you choose the best flea medication, consider your pet’s demeanor. Some pet owners find it challenging to get their pets to take pills. If this is the case, then you might want to consider a topical medication or a chew. Some owners prefer using a flea collar unless their pets cannot tolerate wearing one.

You should also consider how often you need to administer the medication. If your pet fights it, you might want a pill or chew that your pet only has to take twice per year. If your pet cannot sit still so you can apply a topical medication, then you might consider a collar or an edible option.

Some flea treatments have side effects, like vomiting or diarrhea. But, fleas can create more health problems that can be transmitted to humans. You must learn about the best options for your fur baby.

Comfortis and Capstar Similarities

Comfortis and Capstar kill fleas through an oral, chewable tablet. They do not kill flea eggs or ticks. Both tablets start killing adult fleas in 30 minutes. Neither medication will kill flea eggs or prevent more fleas from burrowing into your pet. They only kill fleas that are already at the adult stage.

They are both FDA approved and recommended for pets that are in generally good health. They both have minimum recommended weights, so you should not give these flea tablets to newborn pets. Both medications are made by reputable companies that stand behind their products.

Both Comfortis and Capstar have side effects, but they are mild. Pets might itch as the fleas die. Most of the side effects happen quickly and stop within a few hours. Pets who ingest Comfortis might vomit, while pets that take Capstar might have an upset stomach as a side effect.

Both medications have notable effectiveness. Capstar will kill more than 90 percent of fleas within a few hours. Comfortis is 100 percent effective within a few hours of ingesting the tablet. These two pills will kill fleas and give fur babies quick itch relief.

Since both medications are in a tablet or pill form, some owners have reported struggles getting their finicky pets to take them.

Comfortis and Capstar Differences

Comfortis and Capstar provide flea treatments but in slightly different ways. Licensed veterinarians must prescribe Comfortis, but you can purchase Capstar over the counter. There are various options for cats and dogs.

Capstar has an active ingredient called nitenpyram, which is absorbed into the bloodstream. The active ingredient is harmful to humans. This medication provides immediate relief but has to be taken daily to maintain a flea-free pet. Pet owners usually give this medication to pets that do not spend much time outside.

They give them the meds when they have a special event that requires time outdoors. Owners occasionally struggle to get their pets to take Capstar. The tablet is flavorless, so some pets don’t like it.

Capstar is for dogs that weigh at least two pounds and are at least one month old. There are dosing recommendations for dogs that weigh under 25 pounds, and those that weigh between 25 and 125 pounds. You should talk to your vet if your dog weighs over 125 pounds.

Comfortis has an active ingredient called spinosad, which attacks the nervous system of adult fleas. This preventative medication needs to be taken monthly to keep fleas at bay. This medication is suggested for dogs and cats that are 14 weeks of age or more. The beef-flavored tablet is easy for pets to eat and swallow.

Comfortis and Capstar Pricing Comparison

The two flea treatments have different price points. As Capstar is an over-the-counter treatment, it is less expensive by the box than Comfortis, which is a prescription medication. But, it is more costly in the long run, as each dose works for 24 hours.

Capstar comes in three options, two packages for small cats and dogs, and one option for large dogs weighing over 25 pounds. All three boxes include six tablets.

Comfortis is available in five packages for dogs and cats of different sizes. All five packages have six treatments; each treatment lasts one month. Three of the boxes are designed for dogs and cats, while two of the options are just for dogs.

Overall, the price difference is clear. Per dose, Comfortis costs more. But, if you look at the daily cost, Comfortis is a deal costing between $0.50 to $0.60 per day.

Our Review of Comfortis and Capstar

Comfortis and Capstar both are effective at killing fleas, but they do it differently. If you have an indoor pet and you do not spend much time outdoors, then you might not need to invest in a monthly preventative flea treatment. Your pet might need occasional treatments, so it could be best to have a box of Capstar on hand, just in case.

On the other hand, Comfortis is the best choice for pets that regularly spend time outside. The low monthly cost is worth the relief of having a flea-free pet. Comfortis can have more side effects, and pets are more likely to vomit right after taking the pill. Comfortis also has to be prescribed by a veterinarian, so you must factor in the cost of seeing the vet.

If your pet needs regular flea medication, Capstar is not the right choice. It only lasts for 24 hours, and the cost per dose is between $4 and $5, which can become an unwieldy expense if you are giving it your pet daily.

Both medications can be difficult to give to some pets, especially those that have picky palates. But, since they both only need to be administered occasionally, the struggle is worth the benefit of killing fleas.

Veterinarians recommend both medications, and some suggest that pets can supplement Comfortis with Capstar on an as-needed basis. For preventative flea treatments, Comfortis is the best choice.

If fleas are a big problem in your community, you might want to use both Comfortis monthly, and Capstar when your pet scratches uncontrollably. They can be used together, but the cost of Capstar might make you only use it when fleas are especially problematic.

Flea Treatment FAQs

Which active ingredient is more effective: Nitenpyram or Spinosad?

Both are effective, but one lasts longer than the other. Spinosad comes from soil microbes, making it a natural insecticide that attacks fleas’ nervous systems. Fleas quickly become paralyzed, then die. Spinosad is in Comfortis. Nitenpyram works by blocking the fleas’ nervous systems, which kills them, but does not affect your pet.

What are the side effects of Capstar?

Pets that take Capstar often scratch because of the fleas dying in their fur. Some pets become hyperactive, nervous, or tired. They occasionally might vomit, pant, or have diarrhea. Side effects often happen because of improper dosages.

What are the side effects of Comfortis?

The most common side effect is vomiting. Some pets also experience a loss of appetite, weight loss, and diarrhea. Some become sluggish and tired, too. If you notice your pet behaving abnormally, call your veterinarian.

When do you give these treatments to your pets?

If you live in an area with distinct flea seasons, you should give Comfortis to your pet one month before that season begins. Continue to give it until the end of the season. For people who live in areas where flea season is all year, your pet will need doses every month. You can give your pet Capstar any time that fleas are bothering your pet.

Which treatment is safe for pregnant or nursing pets?

Capstar is approved for pregnant or nursing pets. Talk to your veterinarian if your dog is pregnant, nursing, or breeding before you give a dose of Comfortis.

What flavors do these treatments have?

Comfortis is beef flavored due to a pork-based protein. Dogs with pork allergies should not take Comfortis. Capstar is flavorless.


Both Comfortis and Capstar have places in the world of treating flea infestations in dogs and cats. Comfortis is a long-term, monthly flea treatment that prevents infestations. Capstar is a one-time medication that can be given as needed. Veterinarians often recommend flea treatments to all pet owners, even if pets do not spend time outside.

Capstar is helpful to have on hand, even if your pet does not go outside. Fleas can make their way into homes and can be itchy and uncomfortable for your pet. If your pet happens to have a fluke infestation, Capstar might be the only treatment your fur baby needs.

But, if your pet spends time outside, then Comfortis is a good choice. Your pet will need consistent flea prevention treatments, and for the cost, Comfortis is the best bet. You only have to give it once per month, and it is available in six-dose packages. You do need a veterinarian prescription to purchase Comfortis, while Capstar is available over the counter.

Unfortunately, both flea treatments have side effects that can create short-term discomfort for your pet. Both can cause stomach discomfort, with Comfortis causing vomiting. They both can cause pets to scratch as the dying fleas cause an itchy sensation. But, the short term discomfort is better than the long-term problems that can come from untreated flea problems.

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