(NBC) - It's been dubbed Hollywood's big secret - a magic weight loss pill that can help you drop pounds in a matter of days.
The drug is called Clenbuterol and not only is it illegal for human consumption in the United States, it's not really a diet drug at all.
Whether it's a routine check-up or an emergency call in the middle of the night, equine specialist Dr. Doug Daniels knows all about horses. However, in the last year or so, he's heard that a drug he often prescribes for horses suffering from "the heaves" is now being abused by people.
It's called Clenbuterol and in this country it's illegal for human consumption.
"Initially, prior to 1989 it was used in farm animals like show cattle, to promotion the production of lean body mass," Daniels explained.
What can work for show cattle can also have a similar effect in competitive body builders.
In tabloid reports, Britney Spears has been linked to Clenbuterol. It can also have serious side effects -- both mental and physical.
Right around the time of her breakdown, newspaper stories in London suggested Clenbuterol played a role.
Although illegal, it's readily available. One website promises to deliver Clenbuterol to any country in the world.
After you place an order, you get a confirmation e-mail that reads in part, "We are shipping your order along with kid's toys so it will not be obvious that pharma is being shipped. You will find your purchase inside the pack of wooden pencils."
Two weeks later an envelope arrives, postmarked from Bangkok, Thailand. Just as the confirmation e-mail described, it's filled with cheap toys.
If you look carefully, surrounding the pencils, you'll find pills.
A month's supply of Clenbuterol, a horse drug with human side affects that include death.
"Cardiac arrhythmia, racing heartbeat, chest pain, nausea," Daniels said. "It's a dangerous drug - and something that should not be used in that way - especially not without a doctor's orders or prescription or overseeing."
While Clenbuterol is prescribed by doctors in some countries to treat asthma, it can only legally be used in horses in the U.S.