Published: May 13, 2010 11:58 PM EDT

LEE COUNTY, Fla.-- If you buy flea medicine for your dog or cat, it could end up harming or even killing your pet.  According to the Environmental Protection Agency, in 2008 more than 40,000 dogs and cats were reported to have had bad reactions to their flea and tick medication. 600 of them died.

Eula Storrs only has pictures and two death certificates as rememberances of her dogs, Bear and Snowball.  She tells WINK News a bath with flea shampoo killed her dog, Bear. She says a spot treatment killed her other dog, Snowball, just days later.

"I was in tears, they were my life," Eula tells WINK. "First I was upset because I couldn't believe this was happening to my dogs."

The family's veterinarian said the products were to blame.

"I found out the hard way," Eula says.     

Fort Myers Veterinarian, Richard Carpenter says he has seen first hand pets poisoned by flea drops, shampoo and spot treatments and half of the cases he's treated don't survive.

"The chemicals are the problem, they're poisonous, they're toxic," Dr. Carpenter told WINK.

He says some of the formulas on the market use old technology and are too concentrated.  But despite his and other veterinarians' concerns, over-the-counter spot on treatments are still approved by the EPA and are still sold in stores.

Dr. Carpenter warns that "it's important people understand the truth about what's on these store shelves."

We confronted local pet stores that carry the products and no one would answer our questions on camera.  The company Pet Smart says it won't pull the products because the EPA doesn't require them to and that the products are effective if used properly.

But in a report obtained by WINK News, the EPA admits it doesn't know the exact cause of the bad reactions.  

In an e-mail to WINK news the EPA said, "at this time we do not have adequate data to conduct an analysis to determine whether some active ingredients are worse than others."

But the EPA is increasingly concerned about the large number of incident reports.  It found smaller and younger dogs seemed to be the most at risk.  In some of the cases it studied, the owner bought the wrong medication for their size pet, which proved too toxic.  But in other cases, pet owners say they followed the directions exactly and their pet still reacted badly or died.

Dr. Carpenter explained to WINK, "My concern is the EPA knows these things exist and this problem exist. Why do they not regulate this thing?"       

We asked the EPA why they weren't pulling the products and they said along with not being able to pinpoint a cause for the bad reactions, that "flea and tick products can be appropriate treatments for protecting pets and public health because fleas and ticks can transmit disease to animals and humans."

But the EPA is taking some action right now by ordering pet medication manufacturers to improve warning labels.  The agency promises to monitor new products closely and restrict some ingredients.  The EPA is also launching a campaign to raise awareness and says for small dogs, products need to be less concentrated.

But even with the changes, the EPA still urges pet owners to talk to their vet about these products.

We also got reaction from two top flea and tick medication manufacturers.  Hartz says all of its products meet the strictest EPA standards.  Sergeants says it welcomes the actions taken by the EPA.  Sergeants launched an educational campaign a few years ago to help customers use their products safely and effectively and has taken steps to make the labels easier to read.

To read the complete EPA report on pet medications, click here.