The options are expanding nearly as fast as America's waistline. Here's how to choose.

By Michele Pullia Turk

LAST MONTH'S approval of another prescription weight-loss drug dangles tantalizing new hope in front of the one in three Americans who are obese. But the drugs and their outcomes are tricky. Experts say only severely overweight people should consider taking diet drugs.

"We've got to treat people who have health risks rather than treating people who just want to look good in a bathing suit," says Louis Aronne, M.D., author of Weigh Less, Live Longer (John Wiley & Sons, $14.95) and a professor of medicine at New York Weill Cornell Center.

Keep in mind that none of today's drugs are blockbusters, says Arthur Frank, M.D., medical director of the George Washington University Obesity Management Program, but all make it a little easier for people who are struggling.

You should ask your doctor about the following, particularly before using:

Fat blocker
Newly approved orlistat, sold under the brand-name Xenical for less than $5 a day, blocks absorption of up to 30% of dietary fat. A study published in January's Journal of the American Medical Association found Xenical can help obese people lose weight and keep it off; the drug also can reduce risk factors for heart disease -- for example, lowering "bad" cholesterol. Obese people in a standard diet and exercise program who took the drug lost 19 pounds in the first year, while those who took a placebo lost 12 pounds. Patients who eat less fat are less likely to have unpleasant side effects including flatulence and diarrhea -- a built-in mechanism to discourage overindulging.

Appetite suppressants
Sibutramine, available since 1997 under the brand-name Meridia, seems to help most in the first six months of a diet. "One of the things people have to get used to is that these medications work terrifically well for some people and for others they don't work at all," says Aronne. The pills cost about $3 per day. Meridia's main drawback is that it increases blood pressure, so patients must closely monitor their blood pressure and pulse. Because Meridia is in the same class of drugs as common anti-depressants, Frank sees "very little downside or risk in taking Meridia."

Another appetite suppressant, phentermine, became famous as the "phen" in popular fen/phen prescriptions but lost its luster when fen/phen was linked to heart damage in 1997. Some doctors still prescribe phentermine (cost: $1 a day). Others pair it with the anti-depressant Prozac, but Frank says there's little evidence this "pro/phen" is more effective than phentermine alone.