The biggest test yet of the drug found that it helped people not only drop pounds but also keep them off for two years - longer than any other diet drug has been able to achieve. Cholesterol and other health measures improved, too.

The impressive results from a study of more than 3,000 obese people were presented at a medical conference Tuesday, capping months of anticipation about the new drug, Acomplia, made by the French pharmaceutical firm Sanofi-Aventis.

Doctors called the research exciting and the company, which funded the study, thinks the drug could have blockbuster potential similar to cholesterol-lowering statin drugs.

In a study of 3,040 obese people throughout the United States and Canada, those given the higher of two doses of the drug lost more than 5 percent of their initial body weight, and a third of them lost more than 10 percent.

"They achieved and maintained a weight loss of 19 pounds as compared to 5.1 pounds in the placebo group," said Dr. F-Xavier Pi-Sunyer of Columbia University in New York, who led the research and presented results at the American Heart Association conference.

Those who quit taking the pill in the second year of the study regained most of what they'd lost, suggesting that people might have to take the drug indefinitely to maintain a lower weight.

"We consider this to be a chronic problem. You don't cure obesity, you just improve it," Pi-Sunyer said.

About two-thirds of American adults are overweight or obese, raising their risk of everything from cancer and cardiovascular disease to sore joints and snoring. About a fourth of American adults smoke, which brings many of the same woes.

This is the first diet drug aimed at blocking the "pleasure center" of the brain and interfering with the cycle of craving and satisfaction that drives many compulsive behaviors and addictions. This same circuitry is activated when people smoke marijuana.