NEW YORK (CNNMoney.com) - Roche Holdings, the Swiss drug maker, has hundreds of millions of dollars off its prescription diet drug Xenical, and now GlaxoSmithKline wants to put it on the market as an over-the counter drug.

Xenical, also known as orlistat, has been available in the United States as a prescription since 1999, sold by Roche. The drug works by blocking the body's absorption of fat. In July 2004, GlaxoSmithKline (up $0.24 to $51.61, Research) acquired the rights from Roche to sell the drug in the U.S. over-the-counter. Now all its needs is a green light from the government.

On Jan. 23, an advisory committee for the Food and Drug Administration will vote on whether Xenical should be recommended for the OTC market. The FDA usually follows the advice of its committees.

Bernstein analyst Gbola Amusa said Xenical is safe and that the drug will "more likely than not" get a pass from the FDA. However, Amusa said that Xenical is not an important drug for either Roche or GlaxoSmithKline, despite the nation's obesity epidemic, so little is riding on the FDA panel vote in terms of company sales.

"I'm not convinced this would be a commercial success for Glaxo and Roche," said Amusa. He said that Xenical's biggest obstacle to becoming a big seller are "socially unacceptable side effects like flatulence and oily stools," which result from fat being passed through the body rather than being absorbed.

Roche makes and sells Xenical as a prescription in the U.S. and overseas, with sales totaling $464 million in 2004, and $244 million in the first six months of 2005, the most recent figures available from Roche. The drug is not considered a big earner for Roche, which reported total sales of $12.9 billion in the first six months of 2005, or for London-based GlaxoSmithKline, which reported $27.7 billion in sales for the first nine months of 2005.

Xenical is designed to help obese people lose weight, but its biggest challenge in getting past the FDA as an over-the-counter drug is its potential for abuse in the hands of people with eating disorders who are not obese, said Amusa.

However Amusa did note that Xenical as an OTC would have reduced potency compared to its dosage as a prescription drug.

Any diet drug reviewed by the FDA is likely to go through tight scrutiny, haunted by the ghost of fen-phen, a diet drug combination that was pulled off the market in 1997 after it was linked to heart valve disease. That drug was produced by Wyeth (up $0.54 to $48.18, Research), known at that time as American Home Products. In 1999, the company paid a $3.75 billion settlement to thousands of people who used fen-phen before it went off the market.

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