Special Report: Size zero pill

It's seductive.

"It's a quick way, like in two weeks, that you can drop 10 or 15 pounds," said a male, clenbuterol user.

It's secretive.

"I knew clenbuterol was illegal, but I did it anyway," said a female, clenbuterol user.

And dangerous.

"It made me so nervous and jittery and anxious that I couldn't even really function," said a male, clenbuterol user.

Desperate dieters are turning to a dark underworld of illegal drugs, hoping to slim down fast! Their latest choice is clenbuterol. The drug is used to treat horses with breathing disorders like asthma. It's not meant for humans.

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

But users can't resist its allure. Clenbuterol is nick-named the "size zero pill," because it melts away fat quickly by elevating the heart rate and increasing body temperature.

"If you take enough of it, you can pretty much eliminate the appetite and greatly increase your metabolism, so that the weight loss will occur very rapidly," said Dr. Harrison Pope, a psychiatrist at McLean Hospital.

This young woman, who didn't want to be identified, turned to the drug when she couldn't lose weight on her own.

"I just plateaued alot, and there just wasn't much more I could do," said the female, clenbuterol user. "I got desperate."

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.

"Those pressures can get so much that you overlook the fine print," said a male, clenbuterol user.

But that fine print is screaming danger.

Male Clenbuterol User
"I would lay down in bed at night, and it would feel like my heart would beat out of my chest," said a male, clenbuterol user.

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

"It would make me so hyper and high strung," said a male, clenbuterol user. 

And when taken in high doses, clenbuterol could increase the risk of stroke and heart arrhythmia.

"This was primarily a veterinary drug that was used in veterinary uses, not for people, and we just don't know the full rage of possible effects and dangers that it may have," Dr. Pope said.

But even with those risks, Internet sites are still selling clenbuterol for about the same price as average diet pills.

And even more alarming, most of the Web sites selling the drug are based overseas. So, there's no way to know exactly what you're getting.

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 counterfeit clenbuterol.

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.

"I've learned the hard way that quick weight loss fads are not something that work for my body," said a female, clenbuterol user. 

"I would never take it again," said a male, clenbuterol user. "It made me feel awful."

And if all of those reasons to not take the drug aren't enough, here's another. It eventually stops working. Your metabolism actually shuts down, and you gain back all the weight.

(Copyright 2007 Sunbeam Television. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)