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 here .) "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.
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THE SKINNY: This prescription weight-loss drug acts on the brain's appetite-control center to make you feel fuller faster—so you'll likely eat less, says Madelyn Fernstrom, Ph.D. of the Weight Management Center at the University of Pittsburgh Medical Center. It works by altering levels of serotonin and norepinephrine, two chemicals that help regulate satiety. People on sibutramine lost about 10 pounds more in a year than those taking a placebo, according to a study review.
THE RISKS: Meridia can raise blood pressure, increasing the risk of heart attack or stroke. In fact, it was temporarily banned in Italy, after 50 adverse reactions. And in 2002, the nonprofit group Public Citizen petitioned the FDA to ban it in the United States, citing evidence that Meridia was associated with 29 deaths and hundreds of reactions such as rapid heart rate, high blood pressure, and heart palpitations. The FDA stated that while it wouldn't ban the drug, it would monitor the pill's safety (Abbott, Meridia's manufacturer, maintains that the drug is safe, based on clinical trials of more than 12,000 patients).