Medical Reports: Size Zero Pill

WSVN -- It's seductive, secretive, and dangerous.

Man: "It's a quick way -- like in two weeks -- that you can drop 10 or 15 pounds."

Woman: "I knew Clenbuterol was illegal, but I did it anyway."

These dieters were so desperate they won't let us use their identities or even their voice on TV. They turned to a dark underworld of illegal drugs in hopes of slimming down fast. Their latest choice was Clenbuterol.

The drug, which is sold in pill or liquid form, is used to treat horses with breathing disorders like asthma. It's not meant for humans.

Roni Julien: "This is an illegal drug that, frankly, has been banned in the U.S."

But users can't resist its allure.

Clenbuterol is nick-named the size zero pill, because it melts away fat quickly. It does that by elevating the resting heart rate and increasing body temperature.

This young woman turned to the drug when she couldn't lose weight on her own.

Woman:"I first heard about it at the gym. A lot of trainers have circulated the drug around."

And this entertainment insider thought Clenbuterol would help him fit in in an industry where thin is always in.

For him, the benefits seemed to outweigh the risks.

Man: "Those pressures can get so much that you overlook the fine print."

But that fine print is screaming danger.

Man: "I would lay down in bed at night, and it would feel like my heart would beat out of my chest."

Some of the side effects are heart palpatations, dizziness and the feeling of being hyped up.

Man: "It would make me so hyper and high strung. It made me very sweaty, like I didn't even want to shake someone's hand because my hand would be very sweaty."

Other side effects are downright dangerous.

Woman: "While I was driving, I had my right foot pressed on the brakes, and it started jerking by itself. So, I had to use my left leg to press my brake. If not, I was going to hit the car in front of me."

And when taken in high doses, clenbuterol could increase the risk of stroke and heart arrhythmia -- not to mention the long term affects it can have on your vital organs.

Roni Julien: "You do burn some fat using Clen, however, you burn protein as well. If you think of your heart as protein, and your muscles as protein, you in fact are burning up your organs."

But even with those risks, despite the fact that it's illegal, internet sites are still selling Clenbuterol for about the same price as regular diet pills.

We had dietitian Roni Julien log on, and she quickly found out how easy it is to get the illegal drug.

Roni: "I ordered it on the internet, and it was delivered to my house the next day."

Even more alarming? Most of the websites selling the drug are based overseas, so there's no way to know exactly what you're really getting.

But some users don't stop with the internet. They're even crossing the border.

Woman: "A lot of friends and locals from South Florida go to Mexico all the time, and it's not hard to get in Mexico."

So far, there have been no human deaths directly linked to the product. But, a year ago, at least six horses in Louisiana died after they were given counterfiet Clenbuterol.

Woman: "I've learned the hard way that quick weight loss fads are not something that works for my body."

Both of the users we talked to couldn't handle the side effects and quit the size zero pill a few weeks after taking it.

They have a warning for other desperate dieters.

Man: "I would never take it again. It made me feel awful."