--It seems likely that a new prescription obesity drug with a unique method of prompting weight loss will be hitting pharmacy shelves in the near future.

On Wednesday, a Food and Drug Administration (FDA) advisory panel unanimous recommended that the FDA approve the drug, called orlistat, or Xenical. The FDA usually, but not always, follows the advice of such panels.

"I think this is going to be another option for people who are at medically significant risk from their obesity, but it's not a magic bullet," said Dr. Susan Zelitch Yanovski, director of the obesity and eating disorders program at National Institute of Diabetes and Digestive and Kidney Disorders in Bethesda, Maryland.

Xenical interferes with digestion, reducing the amount of fat absorbed from the diet by 30%. Other weight-loss drugs on the market, such as the recently approved Redux, prompt weight loss by acting on the brain to suppress appetite.

The drug is intended only for those at risk of serious health problems because they are overweight, according to its manufacturer, the Nutley, New Jersey-based pharmaceutical company, Hoffman-LaRoche. Xenical also interferes with the absorption of some nutrients, including vitamin D, vitamin B and beta carotene, so people taking the drug need to consume a multivitamin, as well. And it can cause bloating, gas, and oily or loose stools, side effects that may worsen as the fat content in the diet goes up -- a strong incentive not to gorge on high-fat food while taking the drug.

"If you eat too much fat you're going to feel it," said Yanovski. "I've heard it described as Antabuse for fat."

Clinical trials of the drug suggest that a 220 pound person on a reduced calorie diet who took Xenical three times a day would lose 20 pounds, or 10% of their body weight in a year. Overall, 40% to 57% of patients lost at least 5% of their body weight compared with just 24% to 31% taking a placebo, or inactive medication. Overall, the drug has been tested on 4,000 patients in the U.S. and Europe, for at least two years.

The drug is clearly "not something that people should be taking casually to lose 5 or 10 pounds," Yanovski said. The clinical trials showed that 11 women were diagnosed with breast cancer during the study, compared with just one woman taking a placebo. However, this finding may have been due to chance, or because the weight loss made breast tumors easier to detect, according to the company. Animal studies showed no basis for an excess cancer risk.

"I think there are a lot of unknowns," said Yanovski. "One of the impressive things is that they had two-year data in a large number of patients, which is certainly more than we have had for other studies.