Unlike obesity drugs that suppress appetite, the newly approved orlistat (Xenical) works by partially blocking the absorption of dietary fat. In a recent trial published in the Journal of the American Medical Association, obese dieters on orlistat lost 12 pounds after two years, while a similar placebo group lost less than a pound.

On the downside, orlistat commonly causes intestinal side effects, such as fatty stools, oily spotting, flatulence with discharge, an urgent need to defecate, and frequent bowel movements. It also impedes the absorption of fat-soluble vitamins. Moreover, orlistat has not been well studied in older people - or studied at all for longer than two years. Finally, you still need diet and exercise to make weight loss last: Even the orlistat users regained some lost weight during the study.