If you've visited Internet weight loss sites, chances are you've seen ads for Clenbuterol, "the size 0 pill."

The pill, the only FDA-approved for horses with obstructive airway disease, melts away 6 to 10 pounds a week with no prescription, no exercise and no change in diet.

But the pill comes with some very big risks, according to CBS5.com in San Francisco.

Dr. Kim Mulvihill writes that it elevates blood pressure, and heart rate, raising the risk of arrhythmias and stroke. It can cause tremors, headaches, insomnia and anxiety.

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-- Amanda Barrett, amNY.com