alli (pronounced "al-eye") is the brand name that has been given to low-dose Xenical (orlistat), the first drug in a new class of non-systemically acting anti-obesity drugs known as lipase inhibitors.

Orlistat, which has been marketed in the United States as a prescription weight loss medication since 1999, works in your intestines where it blocks some of the fat you eat from being absorbed and digested. This undigested fat is then removed in your bowel movements.

Absorption of fat is decreased by about 30 percent. Since undigested triglycerides are not absorbed, the reduced caloric intake may have a positive effect on weight control.

While Xenical was developed by Roche, the rights to market Alli as a half-dose over-the-counter drug were acquired in July 2004 by GlaxoSmithKline. The two companies subsequently announced an agreement in April 2005 under which GlaxoSmithKline would market and promote prescription Xenical in the United States as well.

With alli now approved by the U.S. Food and Drug Administration (FDA) for over-the-counter sale, Glaxo intends to begin marketing it in the summer of 2007 as the only FDA-endorsed weight-loss drug available without a prescription.

The most common side effects of prescription strength Xenical are oily spotting, gas with discharge, fecal urgency, fatty/oily stools and frequent bowel movements. All evidence suggests that these same side-effects exist with half-strength alli.

While a number of medical experts have expressed concern over the potential for abuse of an over-the-counter form of orlistat, Dr. Howard Eisenson of Duke University has expressed the opinion that alli's unpleasant side effects should "limit the potential for abuse."

Glaxo also is proposing that over-the-counter sales of alli be restricted to adults 18 and over in an effort to curb misuse by teenagers. Purchasers may be asked to present a driver's license in order to purchase alli, just as they do to buy alcohol or cigarettes.

The name alli was chosen by Glaxo to indicate that the drug, to be effective, must be allied with a weight-loss program. Glaxo's plan is that consumers who purchase alli will also get a guide offering exercise tips, a healthy eating guide, and a fat and calories gram counter. Glaxo is also expected to offer a free behavioral support program on the internet.

Glaxo's Steven L. Burton said studies showed that the over-the-counter dose of Xenical of 60 milligrams, taken thrice daily, enabled people to lose about 80 to 85 percent of the weight lost by those taking the prescription 120-milligram dose.

At the 2005 Annual Meeting of NAASO, The Obesity Society in Vancouver, British Columbia, results were presented of a study that compared half-dose Xenical plus diet to placebo plus diet in patients with a body mass index (BMI) of 25 to 28.

In the 16-week study, low-dose Xenical patients on average lost 5 percent of their baseline weight and while those receiving a placebo but following the same diet guidelines on average lost 3.3 percent.

Safety and tolerability of 60 mg orlistat in this study was similar to that observed in previous studies in a more overweight population.