While millions of Americans wait for over-the-counter diet pill alli, a half-strength version of prescription diet drug Xenical (orlistat), to make it to the shelves of their local pharmacy or supermarket sometime this summer, here is a factlet provided by GlaxoSmithKline to ponder.

In the eight years that Xenical has been on the market, obese and overweight people around the world have tried the diet drug more than 25 million times. Yet, U.S. sales of Xenical peaked in the year 2000 at about $200 million, making it by any standards not a very successful prescription diet drug.

By comparison, analysts are forecasting that prescription diet drug Acomplia (rimonabant) -- on sale in Europe but still stalled at the Food and Drug Administation -- may ultimately ring up annual sales as high as several billion dollars.

Part of the explanation for Xenical's disappointing showing lies in the way the drug blocks absorption of fat, producing side-effects that include oily spotting, gas with discharge, fecal urgency, and diarrhea. These same side-effects can be expected by people who consume too much fat while taking alli.

But the larger reason for the lack of success of Xenical was that most obese and overweight people who took it were disappointed with the relatively small amount of weight they lost -- an amount that certainly will not be greater, and most likely will be less, with alli.

Obese people in too many cases are looking for a miracle, which explains why Americans spend more than $1 billion a year on unproven, quick-fix herbal products and supplements that supposedly will cause unwanted pounds to melt off overnight.

So the challenge facing GlaxoSmithKline -- in selling a nonprescription pill that is only half the strength of Xenical -- lies in building enthusiasm while at the sametime lowering expectations of prospective customers as to what alli can realistically help them achieve.

In a February 8th conference call with reporters, GSK executives and medical consultants repeatedly talked of the health benefits linked to the loss of just 5 percent of a person's bodyweight.

But if that person is a five-foot-three woman who weighs 190 and is yearning to be a size four, is the loss of less than ten pounds while experiencing some gastrointestinal side-effects going to be sufficiently rewarding to keep her coming back to alli?

Glaxo executives expressed the hope that with a several month education campaign -- and by presenting alli as one component of a holistic life-change that includes a healthier diet and more exercise -- 5 to 6 million Americans can be persuaded to try the only FDA-approved nonprescription diet product.

"Because weight loss doesn't happen overnight, we're starting to educate consumers now about the importance of realistic expectations, gradual weight loss and lifestyle changes," said Steven L. Burton, Vice President, Weight Control, GSK Healthcare.

"This is a brand that will be marketed honestly," Burton added.

Now there's a novel approach that will make alli a unique product on drugstore and supermarket shelves. It will be fascinating to see if the weight-loss consumer is ready for it.