An advisory panel for the Food and Drug Administration endorsed a proposal on Monday by GlaxoSmithKline to sell the prescription weight loss drug Xenical over the counter, saying it would provide a safer and more effective alternative to the unapproved diet products that are widely sold.

Xenical, made by Roche and available by prescription since 1999 in the United States, would become the only FDA-approved weight loss drug sold without a prescription, if the agency follows the panel’s advice.

The most notable side effects are gastrointestinal problems ranging from flatulence to loss of bowel control, one reason the drug’s domestic sales last year were only about $100 million.

“The risks seem relatively small, but I do have concern with what we euphemistically call the underwear risk,” panel chairman Dr. Alastair Wood said. “They need to be clearly outlined. … These are real risks that do have social consequences.”

About 50 percent of patients experience some problems, but only about 7 percent had episodes of loss of bowel control, Glaxo officials said.

Patients will be advised to begin taking the drug on a Friday so they can adjust before returning to work. The company will also give advice about clothes that patients can wear to mask the potential problem.

The drug produces moderate weight loss when combined with a diet and exercise plan.

After a daylong hearing, the panel voted 11-3 in favor of the drug’s over-the-counter sale.

The agency usually follows the recommendations of its outside panels of experts, but its final decision could take months.

If approved, orlistat would be the first weight-loss drug sanctioned for over-the-counter sales. Roche will continue selling Xenical regardless.

“We are excited about the potential opportunity to provide consumers with an FDA-approved over-the-counter option that promotes gradual yet meaningful weight loss,” said George Quesnelle, president of GlaxoSmithKline Consumer Healthcare North America.

Limiting use of drug
In six-month clinical trials, obese people who took orlistat lost on average 5.3 pounds to 6.2 pounds more than did those who were given dummy pills. Glaxo wants people to use it for only six months at a time, but as an over-the-counter item, its use would not be policed.

The drug’s effect ends once its use is stopped, said Dr. Julie Golden, a medical officer in the FDA’s division of metabolism and endocrinology products.

A previous study showed a progressive weight gain in patients after they discontinued use of orlistat, she said. Quesnelle said people could resume use or seek help from a doctor if they gain weight.

The panel also raised concern about whether patients would understand more serious risks that affect only a small number of people, particularly organ transplant recipients.

The drug could cause organ rejection by reducing the effectiveness of drugs taken to prevent the rejection.

Remember your vitamins
Xenical must also be taken with a multivitamin, because it blocks the absorption of some vitamins.

Glaxo’s consumer health division licensed Xenical from Roche, its maker, in 2004 with plans to move it to the over-the-counter market.

The company has said it wants to sell Xenical in 60 milligram tablets under the name Alli (pronounced like ally.)

The prescription dose is 120 milligrams. Patients using the over-the-counter drug would be told to take one or two capsules three times a day accompanied by a weight-loss program.

Diet, exercise guide, too
The company said it planned to provide 250 pages of diet and exercise guides along with the product and would provide a 12-month online weight management program free.

A 90-capsule supply will cost about $55, according to Glaxo’s vice president for weight-control products, Steven L. Burton.

He predicted that about five million to six million people would start using the product annually.

Clinical studies have shown that when combined with a diet, nearly 50 percent of patients taking 60 milligrams of the drug three times a day lose 5 percent or more of their body weight in six months, compared with about 26 percent of those taking a placebo.

Abuse concerns
The reviewers also expressed concern about the increased potential for abuse or misuse of a prescription-free version of the drug, especially among bulimics or binge-eaters who could develop vitamin deficiencies due to chronic use.

The company said there was a “very low” potential for abuse, with only four published reports of bulimics using the drug.

More than 22 million people worldwide have used orlistat in prescription form.

British-owned GlaxoSmithKline’s U.S. operations are based in Philadelphia and Research Triangle Park, N.C.