NEW ORLEANS – An experimental pill that offers the fairy-tale promise of helping people lose weight and quit smoking has gathered even more stardust.

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 had 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.

It’s been devilishly difficult to develop effective treatments for either problem. Diet drugs in particular have a checkered history, most notably the withdrawal from the market in 1997 of the popular “fen-phen” drug combination after users developed heart valve problems.

Drugs now on the market either are designed for short-term use or have distasteful side effects like bowel problems that make many shy away from them.

Acomplia’s maker thinks it will avoid those problems by attacking obesity in a novel way, and plans to seek federal approval for it next year.

It’s 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 pot.

“Weight regulation is really kind of an addictive behavior,” said Dr. Robert Eckel, an expert on metabolism from the University of Colorado Health Sciences Center who had no role in the study.

It involved people who either were severely obese or were moderately obese and also had another heart-related health problem such as low “good” cholesterol, high blood pressure, or high blood sugar.

They were given nutrition advice and urged to cut 600 calories a day from their diet, and were randomly assigned to get either a 5- or 20-milligram dose of Acomplia or fake pills. Neither they nor their doctors knew who had received which.

After one year, those on the higher dose had lost an average of 19 pounds – the same result found in two smaller studies of the drug reported earlier this year.

The new study went on to test whether staying on the drug kept people from regaining weight. Those who took Acomplia during the first year were redivided to either continue on it or get fake pills for the second year.

At the end of the two years, 62.5 percent of people on the higher dose had lost 5 percent of their body weight compared to 36.7 percent on the low dose and 33.2 percent on fake pills.

Waistlines shrank 3.1 inches with the higher dose, 1.9 inches with the lower one and 1.5 inches for those on fake pills.

HDL or “good” cholesterol rose 24.5 percent on the higher dose, 15.6 percent on the lower one and 13.8 percent on fake pills. Triglycerides also fell according to dose.