NEW YORK - You won't lose weight in your sleep or shed pounds while eating anything you want -- that's the sobering message from the maker of a weight loss pill poised to hit shelves next month.

GlaxoSmithKline on Tuesday opened an educational exhibit in New York City to prepare the country for alli, the first over-the-counter diet pill approved by the Food and Drug Administration.

While the cautionary marketing approach may not trigger stampedes to the counter, analysts say the drug's fate hinges on the pharmaceutical giant's ability to convince people that diet pills aren't a magic bullet.

"People's hopes are ridiculously high when it comes to diet pills. That leads to disappointment and bad word of mouth," said Steven Brozak, an analyst with WBB Securities.

That's just what happened to the prescription version of the drug, Xenical by Roche Holding, which contains twice the dosage. People were let down when it failed to deliver dramatic results and the drug never really caught on, Brozak said.

GlaxoSmithKline has apparently learned the lesson and is counting on alli to become a star money maker. The company is spending US$150 million on marketing alli this year, making it one of the drug maker's biggest campaigns to date.

"We've done everything to go out of our way to be honest," said Steve Burton, vice president of the weight control division at GlaxoSmithKline Consumer Healthcare. "We're taking a very different approach than the fad diets people are constantly exposed to."

In clinical trials, the FDA says that people using alli lost an additional 2 to 3 pounds for every 5 pounds lost through diet and exercise. The FDA approved alli to be sold over the counter in February.

When taken with meals, the drug blocks the absorption of about one-quarter of any fat consumed. That fat -- about 150 to 200 calories worth -- is passed out of the body, potentially resulting in loose stools.

About half of patients in trials experienced gastrointestinal side effects, including leakages and oily discharges.

GlaxoSmithKline is frank about those unpleasant effects, which it says can be controlled if the drug is used properly. The campaign stresses the importance of keeping meals under 15 grams of fat to avoid effects.

Educational materials even recommend people start the program when they have a few days off work, or to bring an extra pair of pants to the office. Experts say a failure to adequately prepare consumers about the effects contributed to Xenical's limited success.

The alli event comes a day after the company's shares dropped almost 8 percent when a report this week found the company's widely prescribed diabetes pill raised the risk of heart attacks and possibly death. Some experts called it another Vioxx-like example of the U.S. government failing to protect people from an unsafe drug.

Glaxo shares rose 1.4 percent to $53.90 on Tuesday.

Alli only affects the digestive system, Glaxo says, and is the only safe over-the-counter diet drug that's been shown to work.

The company estimates 5 million to 6 million Americans a year will buy the drug, translating to at least $1.5 billion a year in retail sales.

The drug will come in "starter kits" containing a food journal, a healthy eating guide and a fat and calorie reference guide. A 60-capsule kit will cost about $50 while a 90-capsule pack will cost about $60. Recommended usage is one to three pills daily.

Labeling indicates alli is appropriate for anybody who is overweight, or has a body mass index of 25 or higher. A body mass index over 30 is considered obese.

Two-thirds of the U.S. population is estimated to be overweight or obese.

Just how many people find alli's benefits worth the cost of the drug is the "million dollar question," said Kelly Brownell, a food policy researcher at Yale University.

Diet drugs don't deliver the big results most people expect, and are only effective when used along with diet and exercise, Brownell said.

The alli exhibit in New York City -- featuring plates with sensible portion sizes and an interactive Web site -- encapsulates the drug maker's marketing emphasis on that need for diet and exercise.

To prepare for alli's launch in mid-June, the company ran television spots directing viewers to a Web site where they could learn more about the drug. A retail book was also made available. The idea, Burton said, was to give "people some pause" and time to learn about the drug.

The message that alli isn't an easy fix marks a step in the right direction for pharmaceutical companies, said Michael Santoro, a professor of business ethics at Rutgers University.

"One of the things we've seen so often in advertisements is that a drug can be an alternative to a healthy lifestyle," Santoro said.

Still, he questioned whether a diet drug had any role in a campaign about healthy lifestyles.