In tests on more than 3,000 people throughout the United States and Canada, those who were 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 study and presented results at an American Heart Association conference.
Those who got the lower dose fared just slightly better than those given fake pills. About a third of them lost 5 percent of their weight and about one-fifth lost 10 percent.
The drug's maker, the French pharmaceutical firm Sanofi Aventis SA, has named the drug Acomplia and plans to seek federal approval for it next year.
Acomplia is first treatment 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.
"What we have here now is essentially a brand new mechanism to treat an epidemic of staggering progression," said Dr. Douglas Greene, vice president of regulatory affairs for Sanofi Aventis.
"What the medicine appears to do is help (people) stick with diets, (and) there is an independent effect on fat cells that helps them to lose weight," says Dr. Lou Aronne, an obesity specialist and Director of the Comprehensive Weight Loss Center at Weill Cornell Medical Center in New York. He helped test the drug.
Aronne tells CBS News' The Early Show that Acomplia may also help people stop smoking. "There are other studies, besides this one, that show Acomplia can reduce the number of people who smoke," he notes. "So if you're smoking, it cuts the number of people who smoke in half if you're making the effort to stop smoking."
"The results are very encouraging. The safety profile looks good. It seems like people tolerate the medication," said Dr. Sidney C. Smith Jr., a University of North Carolina cardiologist who had no role in the study.
"It would be nice if this could be used as a jump-start" to get people to permanently change lifestyle habits so they didn't have to depend on a drug for the benefits, he said. "The more we can change behavior and modify risk factors in that manner, the better."
Sanofi Aventis was created by the merger earlier this year of Sanofi-Synthelabo SA and Aventis SA. It is the world's No.3 pharmaceutical company by sales, behind U.S. giant Pfizer Inc. and Britain's GlaxoSmithKline PLC. The company's high-profile drugs include anti-thrombosis treatments, Lovenox and Plavix.