The Moon-based consumer division of pharmaceutical giant GlaxoSmithKline will make its case to federal regulators today for selling the nation's first over-the-counter version of a prescription weight-loss drug.

The public hearing of two committees that advise the Food and Drug Administration will culminate in a vote on whether Glaxo should be allowed to sell a lower-dose version of Xenical at retail outlets. The product would sell with the name Alli -- pronounced "ally," as in a helper for dieters.

The stakes at the suburban Washington, D.C., meeting will be high for Glaxo's North American Consumer Healthcare unit, which agreed in 2004 to pay Switzerland's Roche Holdings Inc. $100 million for the rights to sell the obesity drug over the counter. The vote, and subsequent decision by the agency, will be the latest test of how FDA is weighing concerns about expanded access to medicines and drug safety.

A few years ago, FDA had a stated goal of increasing the number of prescription drugs that switch to over the counter, which can be helpful for companies looking to extend the profit-generating potential of name-brand drugs. Switched drugs can be good news for purchasers of medications since nonprescription products tend to sell at lower prices.

But in the wake of the 2004 withdrawal from the market of the arthritis medicine Vioxx, the FDA has faced criticism that it must do more to promote safety. The influence of the "safety camp" was seen by some as a factor in the early 2005 decision by two advisory committees that voted against the over-the-counter switch of Mevacor, a popular cholesterol drug.

Nonetheless, Randy Juhl, the former dean of the pharmacy school at the University of Pittsburgh, believes the Xenical switch to have "good potential."

"From a public health perspective, there are a lot of us living off the fat of the land, so obesity is a growing problem -- pick your pun," said Mr. Juhl, now a Pitt vice chancellor and a founding member of the FDA's nonprescription drugs advisory committee in the 1990s.

Glaxo officials will stress the public health message at today's hearing.

Sixty-five percent of the adult population is either overweight or obese, and many don't typically visit a physician to talk about weight problems, said George Quesnelle, president of Glaxo's Moon unit.

When the company made over-the-counter products from the smoking cessation drugs Nicorette and Nicoderm, Glaxo proved the theory that more people will try certain pharmaceuticals if they don't first have to obtain prescriptions, he said.

Xenical had sales of $102 million in the United States during 2004, according to IMS Health.

Consumers already are spending $1 billion annually in the over-the-counter market on dietary supplements for weight-loss that are not proven to be effective, Mr. Quesnelle said. Some could be unsafe, he added.

"We have the opportunity to provide the first FDA reviewed and approved over-the-counter option that can help people lose weight and make changes to their lifestyle and diet," said Steve Burton, Glaxo's vice president of weight control.

Alli would be sold in a starter kit that includes guidance to help people make the diet and lifestyle changes necessary to lose weight.

Glaxo will present studies that show dieters using the over-the-counter version of Xenical lost 50 percent more than those who just made lifestyle changes. Whereas prescription Xenical comes in a 120 mg dose, Alli would be sold in a 60 mg dose -- half the amount, but still 80 to 85 percent of the efficacy, Mr. Burton said.

Mr. Burton, who himself uses Xenical, said the lower dose helps patients control side effects that can include increased trips to the bathroom, loose stools and more gas.

The drug works in the digestive system to block about one-third of the fat in the food from being digested. In some cases, Xenical users are unable to control bowel movements, particularly after meals containing higher amounts of fat than are recommended.

Communicating the risk of side effects is one of the marketing challenges involved with taking the drug over the counter, said Mr. Juhl, the Pitt official.

"When someone who is taking this drug consumes food that is high in fat content, diarrhea can ensue," he said. "It's not a particularly dangerous side effect. It's just one that is unpleasant."

While Xenical has a long track record that includes numerous safety studies and millions of users, some question whether safety concerns will preclude the OTC switch.

"My bet would be against it," said Joshua Cohen, an economist with the Tufts Center for the Study of Drug Development. Mr. Cohen added, though, that he was wrong last year in predicting that the committees would recommend switching Mevacor, the cholesterol drug.

Bob Wanovich, manager of clinical services and product development at Highmark, the region's dominant health care insurer, said he also doubted that the committees would endorse the switch.

Mr. Wanovich said he was curious to see the company's data on how effective the drug is at a lower dose.

More to the point, because Xenical users are counseled to take vitamins because the drug blocks some vitamin absorption, Mr. Wanovich questioned whether the committees would support making the drug available without guidance from a physician.

Health plans have been proponents of some OTC switches because they drastically lower prices, and therefore provide relief to a health plan's pharmacy budget. But health plans are less interested in the Xenical switch, he said, because the majority of employer-sponsored health plans don't cover the drug.

Mr. Burton, the Glaxo official, said the lack of health plan coverage for the drug is one reason consumers might be interested in the switch. Whereas a one-month supply of Xenical can cost between $150 and $200, the starter kit for Alli, with a comparable number of capsules, might sell for about $55.

While it's always sensible for dieters to take vitamins, Xenical studies suggest that people who didn't do so nonetheless stayed within the healthy range, Mr. Burton said.

As for side effects, Dr. Saul Shiffman, a research professor at the University of Pittsburgh, said a study he conducted in support of Glaxo's application found that half of drug users experienced no side effects. The vast majority of those who did were able to manage them by changing their diet or the way they took the medication.

"Putting a product like this over the counter can dramatically increase effective treatment for a lifestyle risk factor, and improve the public health," Dr. Shiffman said.