Highly encouraging results reported November 9th from the largest trial to date of the new diet drug rimonabant (Acomplia) were greated with a mixture of excitement and caution by the medical community.

Data from a two-year study of rimonabant showed the drug helped obese patients lose four times as much weight as those on a placebo and enabled them to keep it off, while also shrinking their waistlines, increasing their good cholesterol, lowering their triiglycerides and improving insulin sensitivity.

Add to that the news that rimonabant side effects seemed relatively minor and one could anticipate the excitement many researchers expressed about a drug that seems to good to be true.

Dr. Robert H. Eckel, president-elect of the American Heart Association, described the research as "very robust and conclusive," and said the news was particularly encouraging given that other approaches have not succeeded in helping patients maintain weight loss for longer than a few months or a year.

Dr. David Haslam, Chairman of the National Obesity Forum in the United Kingdom, termed the test results "very exciting."

“This is a completely unique drug and these are very impressive results," Haslam said. "We are seeing very significant weight loss and the risks of heart disease very much reduced. That is a powerful combination."

"This is a unique drug, a combination of a lifestyle drug that also has medical necessity in terms of improving overall health," said Dr. Marrick Kukin, a cardiologist from St Luke's-Roosevelt Hospital in New York.

"The results are very encouraging," agreed Dr. Sidney Smith Jr., a University of North Carolina cardiologist. "The safety profile looks good. It seems like people tolerate the medication."

But a number of medical researchers attending the American Heart Association scientific meeting where the results were presented -- and those contacted by reporters outside the meeting -- tempered enthusiasm with caution, with several suggesting that much more safety testing is needed.

Several researchers expressed misgivings over the fact that trial participants who were taken off rimonabant after the first year regained most of the weight they had lost in the second year, with only those who continued taking rimonabant maintaining their weight loss.

"One problem is to maintain the weight loss, you have to keep taking the drug," said Dr. Norman Edelman, medical advisor to the American Lung Association.

Dr. Joseph Hayes of Weill-Cornell Medical College in New York suggested that since weight loss for patients taking rimonabant seems to mostly take place in the first year, a follow-up drug may be needed.

"One drug may ultimately not get the job done," agreed Eckel, an expert on metabolism from the University of Colorado Health Sciences Center.

Other researchers noted that most of the patients who took rimonabant in the study -- even after losing five to ten percent of their body weight -- remained overweight at the end of the study period.

"None of these drugs in development is going to be the magic bullet," said Dr. Ernst J. Schaefer, a Tufts University nutrition researcher. "In a 300-pound person who loses 10 percent, that person still weighs 270 pounds."

Several researchers suggested that while side effects from rimonabant in the clinical trials conducted thus far seem relatively minor, more testing is needed.

"We need more safety data, especially among young people," said Robert Bonow of Northwestern University.

Dr. Michael Crawford, professor of medicine at the University of California-San Francisco, said "nobody's going to touch this drug without long-term safety results." Crawford said he would want to see at least five years worth of safety data before prescribing rimonabant.

Dr. Joseph Hayes of Weill-Cornell Medical College in New York also called for a lot of additional testing.

But like many researchers, Hayes conceded he was impressed with the way rimonabant seems to work. The human body is not easily fooled, Hayes said, but with rimonabant, "for some reason the desire to just eat, eat, eat just gets turned off.

"I don't understand that, but if it works, that's great," Hayes added.

For more details on results of the RIO-North America study, please CLICK HERE.