Rimonabant went on sale in Europe in July, and U.S. approval is pending before the Food and Drug Administration. The drug works in a new way, suppressing the appetite by targeting the brain cells involved in the "munchies" familiar to marijuana users.
"The use of rimonabant after one year produces modest weight loss of approximately 5 percent" of body weight, found reviewers led by Cintia Curioni, at the State University of Rio de Janeiro, in Brazil. "Compared with placebo, a 20-milligram pill produced a 4.9 kilogram greater reduction in body weight in trials with one-year results."
This translates to weight loss of a little under 11 pounds.
The review looked at four randomized controlled trials comparing rimonabant at two dosages and with placebo, after one or two years of treatment.
Participants, all overweight or obese, followed a "mild" low-calorie diet, adjusted for individual body weight.
Only the higher dose -- 20 milligrams -- had significant impact on weight, waist circumference, cholesterol levels and blood pressure.
However, the higher dose brought on more, and more serious, side effects than both the lower dose and placebo.
The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates research in all aspects of health care.
Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing trials on a topic.
The rimonabant studies took place in 350 trial centers in the United States, Canada and Europe.
The 6,625 participants were at least 18 years old and overweight or obese. One study focused solely on people being treated for type 2 diabetes; another comprised people with high cholesterol or high blood pressure -- important factors in heart disease risk .
The authors described the weight loss pattern: "After the 36th week, the level of weight loss decreased and the body weight was maintained practically until the end of the studies." One study evaluated data after two years: "Patients who stayed on 20 mg rimonabant seemed to maintain their weight loss, while those who were re-randomized to placebo gained significant weight."
People on the larger dose lost an average 1.5 inches on their waistlines. They also showed a slight dip in blood pressure. The higher drug dose significantly lowered blood lipids (fats) and increased high-density lipoprotein ("good" cholesterol) by 3.5 mg/dl compared to placebo.
But on the flip side, side effects included nausea, dizziness, headache, joint pain and diarrhea. More serious side effects included psychiatric and nervous system disorders.
Obesity drugs, which often come on the market with great fanfare, can end up being withdrawn in a flurry of lawsuits -- like Fen/Phen -- or simply produce underwhelming results for people expecting a magic bullet.
"Every time a new drug comes along, it gets a lot of attention. The natural course is that people who want it will try it, and people with have some lackluster results," said Kelly Brownell, Ph.D., director of the Rudd Center for Food Policy and Obesity at Yale University.
"Few people lose enough weight to make themselves happy, more lose enough weight to get some medical benefit but overall results for most treatments for obesity are disappointing," Brownell said.
Rimonabant has been billed for several years as a potential panacea for the most troublesome of habits – obesity, smoking and possibly alcohol addiction. Studies on its use in smoking-cessation studies are currently under way.
Curioni's team compared its results to a previous review of orlistat and silbutramine, the only drugs approved in the United States for long-term obesity treatment:
"The weight loss associated with rimonabant was slightly greater compared to that related to silbutramine use, with more positive impact on cardiometabolic risk. The effects compared with orlistat appear to be greater weight loss and less frequent adverse effects."
No head-to-head comparisons had been done at the time of the review.
The biggest difference may be in how rimonabant works, by blocking the cannabinoid receptors in the brain. Brownell called rimonabant's ability to suppress munchies "an interesting finding. The issue of food and addiction hasn't been explored very much; it should be."
The review authors noted that the four reviewed studies were sponsored by Sanofi companies. With the studies all being sponsored by the drug-maker, results "probably represent a best-case scenario," Brownell said.
None of the studies analyzed drug costs. "The fundamental problem is that even if one of these drugs caused significant weight loss, the cost would be so prohibitive that it wouldn't be worthwhile on a public health basis," Brownell said. "And only a few people would be able to afford them."
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