The first diet drug aimed at helping the growing number of fat Americans lose weight without seeing a doctor moved one step closer to U.S. approval on Monday after a health advisory panel endorsed the idea.

Called Alli, GlaxoSmithKline's low-dose version of the prescription drug Xenical is generally safe and effective for adults when used for six months, the U.S.  Food and Drug Administration's advisers said.

The FDA will consider the panelists' advice as it decides whether to allow easier access, but usually follows their recommendations.

If approved, it would be the first proven weight-loss drug to be sold over the counter at a time when two-thirds of Americans are overweight or obese.

Panel chairman Dr. Alastair Wood said risks with the drug were low, and people would be better off taking Glaxo's drug than any of the countless, unapproved dietary supplements on the market.

"Is it better to be taking caffeine compounds or this? Probably this," said Wood, a professor of medicine and pharmacology at Vanderbilt University in Nashville, Tennessee.

Company studies showed patients taking Alli lost 1.8 to 2.4 kilograms, or about 4 to 5 pounds, more than those taking a placebo after six months.

Some members voiced concerns about repeated and long-term use.

"I don't think there's been any long-term effectiveness shown," said panelist Dr. Neal Benowitz, a professor of medicine, psychiatry and biopharmaceutical sciences at the University of California in San Francisco.

Dr. Ruth Parker, a professor at Emory University's School of Medicine in Atlanta, said she was concerned about "use and abuse" of the drug among teenagers and others. She added people would be better off focusing on diet and exercise.

Glaxo bought U.S. rights to Xenical from Roche Holding AG last year and hopes to sell a 60-milligram dose of the 120-milligram prescription version. The drug, known generically as orlistat, helps prevent fat from being absorbed by the body.

That process can cause gastrointestinal problems such as oily stools, rectal discharge and excess gas, and about half of all patients experience them.

Glaxo officials told the panelists the lower dose and a low-fat diet reduced side effects.

"There is no magic pill for weight loss, and orlistat is definitely not a magic pill," John Dent, the drugmaker's senior vice president for research and development, said. "Orlistat is a tool that will help people control their calorie intake and modify their diet."

Side effects have helped keep sales of prescription Xenical low, at about $460 million worldwide in 2004.

George Quesnelle, president of GlaxoSmithKline's North American consumer unit, said nonprescription sales could boost that, reaching five to six million Americans each year. The prescription-strength version would remain available.

He did not say when the company expected the FDA's decision, but said he hoped to see the product on store shelves later this year.

Mehta Partners analyst Shaojing Tong said he was skeptical that over-the-counter status would jump-start sales, given the side effects and lack of insurance coverage for nonprescription medicines.

"I don't see how it will revive sales dramatically," Tong said.

Before the panel vote, Glaxo shares rose 1.12 percent, or 56 cents, to close at $50.71 on the  New York Stock Exchange, after earlier closing almost unchanged in London.