Is Frontline Safe for Pets?

Written by eric feigenbaum
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Is Frontline Safe for Pets?

In the warmer months of the year, it can be so much fun to be outside with one's pets. These are also the times of year when our beloved furry friends are most at risk for fleas, ticks and other parasites. In the past decade and a half, new and effective products have come on the market that require only quick, easy, topical treatments that can last for a month. Many of these products, including Frontline Top Spot and Frontline Plus, promise to also prevent flea eggs from hatching.

What is Frontline?

Frontline is a "top spot" flea and tick treatment made by Merial. The treatment involves putting the entire contents of a Frontline packet through the fur and onto the skin of dogs or cats on a spot between their shoulder blades. Hence the "top spot" name. From there, Frontline kills fleas and prevents their return, while Frontline Plus also kills flea eggs. The active ingredient, Fipronil, is considered responsible for the outcomes, and in Frontline Plus, Methroprene is the additive for the egg killing. Merial claims Frontline is waterproof and that, within 12 hours of application, fleas start to die off and their life cycle broken. Despite whatever activities the treated pet may undertake, Front line's protection is supposed to last for a full 30 days.

Is Frontline Safe for Pets?
Frontline Packets


The U.S. Environmental Protection Agency approved Frontline for flea protection use on dogs and cats in 1996. Later in 2003, the EPA cleared Frontline for use on pregnant and lactating dogs and cats, dogs of any size (except puppies and kittens under eight weeks of age), treatment of lice on dogs and cats, and treatment of sarcoptic mange on dogs. And while the EPA has cleared Frontline for all these uses, the EPA's Pesticide Division also notes in a review of Frontline and Fipronil that the key chemicals in Frontline are neurotoxins and have potential for long-term nervous system and thyroid toxicity after long-term exposure at low dosages.

Adverse Reactions

Merial warns on its Frontline website that skin irritation at the site of treatment is a possibility among some animals using Frontline. It also admits Frontline is a chemical pesticide. A review of Frontline by the EPA---which approved the product's use---also found that the manufacturer probably understated potential adverse reactions. In many pets, skin irritation reactions went significantly beyond the site of treatment. The review also showed sloughing and even chemical burns.

Is Frontline Safe for Pets?
An adverse reaction to Frontline

Long-Term Issues

However, many animal safety groups feel that Frontline may have more adverse effects than immediate reactions. Fipronil is a neurotoxin. And while Merial claims that Frontline stays solely within the skin and does not penetrate throughout the body---other studies, namely one conducted by the EPA's Dr. Virginia Dobozy found, "significant amounts of radiolabelled fipronil were found [not only] in various organs and fat...[but they were also] excreted in the urine and feces and were present in other parts of the body...which demonstrated that the chemical is absorbed systemically." Such findings raise concerns among many animal activist and consumer rights groups that Frontline may have long-term neurological effects. Dr. Dobozy's studies singled out thyroid as an area where Fipronil may spur cancer after long-term use.


Frontline can only be purchased through a licensed veterinarian's office. Pet owners concerned about appropriateness of the product for their pets as well as the short- and long-term effects of Frontline should talk about it with their vets. Merial's Frontline website says the company chose to distribute Frontline through vets specifically so that veterinarians can make informed judgments about whether the product is safe and appropriate of an animal---and, in this way, puts much of the onus of responsibility for the product's use and safety onto animal health care professionals.

Is Frontline Safe for Pets?
Only vets can sell Frontline

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