Comfortis is a prescription flea treatment in the form of a monthly, chewable tablet. Although it kills only adult fleas, it keeps working all month, taking out new fleas as they develop. As a result, most vets and users say it's effective enough to wipe out an infestation all by itself. Although most pets can use this drug with no side effects, it can cause vomiting, and on rare occasions more serious complications might develop.
Vets praise its effectiveness. Eric Barchas, vet-in-residence at Dogster.com, considers Comfortis the most effective flea treatment available for dogs. He says most owners who try it -- including himself -- "never look back." The vets at Twin Maples Veterinary Hospital in Ohio say Comfortis kills adult fleas in as little as 30 minutes and its effects last a full month, killing new fleas as they develop before they have a chance to reproduce. Pet owners who review Comfortis at 1800PetMeds.com are generally enthusiastic about its effectiveness as well. Many of them say it worked when all other flea treatments failed -- including other vet-prescribed products.
Use with caution. The biggest downside of Comfortis is the relatively high rate of side effects. Vomiting is the most common problem, and Barchas admits that "a small proportion" of dogs will be unable to use Comfortis for this reason. However, the reviews we consulted from users included rare reports of more serious side effects as well, including some who blamed the treatment for the death of their pets. Dogs are more likely to develop serious side effects than cats. Although these reactions are rare, they're also hard to predict. As a result, we would advise using Comfortis under the supervision of a vet, and then perhaps only if other treatments have failed.
May take some coaxing. Most pet owners find Comfortis easy to use. Users like the fact that, unlike topical treatments, it doesn't have any odor or leave a greasy residue on the pet's fur. However, a few pet owners say getting the pet to take the pill can be tricky. Some users say their pets ate the beef-flavored tablet right out of their (the owners') hands, but others say they had to resort to tricks like slipping it in a "pill pocket" or grinding it up and mixing it with peanut butter.
We found more than 900 reviews for Comfortis at this online pet pharmacy, with ratings averaging 4.5 stars out of 5 overall. While most owners find it effective and easy to use, there are also complaints about side effects -- some of them serious or even deadly. The site posts a warning that lists possible complications, in decreasing order of likelihood.
Review: Comfortis, Contributors to 1800PetMeds.com, As of December 2013
At Dogster.com, Eric Barchas, a veterinarian with over a decade of experience, says Comfortis is highly effective and won't cause skin problems as topical treatments can. However, he warns that it causes some dogs to vomit, so it's not suitable for everyone.
Review: Ask a Vet: Is Your Flea Control Product Hurting Your Dog?, Eric Barchas, April 2, 2013
3. Twin Maples Veterinary Hospital
Vets at Twin Maples Veterinary Hospital say Comfortis is "palatable, easy to give and starts to kill fleas in 30 minutes." They also praise its convenience, since it can't rub off on people or furniture as topical treatments can. The article notes that vomiting is the most common side effect.
Review: A Dayton, OH Veterinarian Discusses Flea Control: Taking Aim on Fleas, Staff of Twin Maples Veterinary Hospital, Not Dated
Veterinarian Carol S. Foil says that Comfortis is "very useful for flea allergic pets" due to its "rapid kill rate." This article was written shortly after Comfortis first came onto the market and does not mention the drug's side effects.
Review: Flea Control, Carol S. Foil, Not Dated
This directory from the Natural Resources Defense Council rates Comfortis one of the safest flea treatments available. Editors say it poses little danger to either pets or humans, but they note that "long-term studies have not been conducted." They recommend consulting a vet before using any flea treatment.
Review: GreenPaws Flea and Tick Products Directory, Editors of SimpleSteps.org, Not Dated