Do Diet Pills Really Work?

Diet drugs have come a long way since the addictive amphetamines of the 1950s. And while each new generation of skinny pills has so far proven more dangerous than effective — remember fen-phen and ephedra? — experts continue their search for a safe diet pill that works. Enter Alli, a new formulation proven to block dietary fat absorption; as of this month, it will be available at your local drugstore, no prescription required. Also on the horizon: the awaited FDA approval of Zimulti, a new prescription pill that not only promises to help slim you down but also improve cholesterol.

But while these pills offer hope for trimming America's ever-expanding waistline, experts caution that there's no miracle potion out there to automatically shrink you back into your college jeans. "These diet drugs work only if you also change your lifestyle, and that means following the same old advice of dieting and exercising," says Caroline Apovian, M.D., of the Nutrition and Weight Management Center at Boston University Medical Center. The medications also come with some real health risks, ranging from nausea and diarrhea to hypertension and depression. Here's the scoop on the five newest weight-loss pills on the market.

Alli (orlistat)

THE SKINNY: Created originally as the prescription drug Xenical, orlistat is now available in a lower-dose version, Alli, which was granted FDA approval to be sold over the counter earlier this year. The drug, which you take up to three times a day with meals, prevents you from digesting 25 percent of the fat you consume (by attaching to some of the enzymes responsible for breaking down fat from food). The amount of fat calories blocked will depend on how much fat you eat, but most patients block 100 to 200 calories per day.

So, how does that play out in pounds? Subjects who took Alli for six months lost 50 percent more weight — say, 15 pounds versus 10 — than those who only dieted, according to a study done by GlaxoSmithKline (GSK) Consumer Healthcare, the drug's manufacturer. It also appeared to inspire positive lifestyle changes: "We found that 80 percent of Alli-takers really stuck to a reduced-fat diet, and 50 percent started exercising for longer periods of time," says Vidhu Bansal, director of Medical Affairs at GSK Consumer Healthcare. A starter pack of Alli — which includes a month's supply of pills, a dietary guidelines guide, a calorie and fat counter, and a food journal — costs about $54.

THE RISKS: If you eat too much fat (more than 30 percent of your calories, or roughly 15 grams of fat per meal), you'll likely experience loose, oily stools, since the excess fat that is blocked from absorption is quickly excreted. "My patients on Xenical often find that when they eat a high-fat meal, several hours later they may have diarrhea or loose stools. In extreme cases, they can't control their bowels — they'll leak all over their pants," says Caroline Cederquist, M.D., a spokesperson for the American Society of Bariatric Physicians (ASBP). (People who took Alli were less likely to experience these side effects.) Taking either drug may also put you at risk for vitamin loss. "You need enough fat in your diet to absorb fat-soluble vitamins such as A and D," adds Loren Wissner Greene, M.D., an obesity specialist at the New York University School of Medicine in New York City.

IS THIS PILL FOR YOU? Alli is intended for people who are overweight, generally defined as those with a body mass index (BMI) — a measure of body fat based on height and weight — of at least 25. (You can calculate your BMI at nhlbisupport.com/bmi.) "Alli, like Xenical, will be useful for people who eat out often and don't have much control over the amount of fat they are served," says Cederquist. "So if you eat more fat than you intended, you'll get rid of it." The drug also works as a splurge deterrent — the side effects are so unpleasant that you'll want to avoid fatty foods. But experts do have fears about misuse: "I worry that a slim woman who just wants to lose 5 pounds to fit into her bikini will use it as a way to eat anything she wants while still getting skinnied up," says Greene. The problem with this? A normal-weight woman who takes Alli places herself at an unnecessary risk of suffering side effects such as loss of bowel control and vitamin loss, whereas for an overweight woman, the health risks of carrying around extra pounds — such as heart disease and diabetes — may outweigh these side effects.