Rimonabant, discovered and developed by French pharmaceutical company Sanofi-Synthelabo, is a new drug thas has shown great promise in trials for the treatment of obesity and related metabolic risk factors.

Rimonabant was on the market in Europe for more than two years, being sold under the trade name Acomplia, before it was withdrawn by Sanofi. It never has been approved in the United States, where Sanofi was hoping to market it as Zimulti.

Rimonabant works by blocking the CB1 receptor, one of two receptors found in a newly described physiological system called the Endocannabinoid System (EC System), believed to play a critical role in the regulation of food intake and energy expenditure.

The receptors are present on the surfaces of many cells throughout the body, including fat cells -- which are involved in lipid and glucose metabolism -- and those in the hypothalamus, the brain region that is thought to determine appetite.

Cannabinoids, chemical compounds produced by your body, latch on to the CB1 receptors, which are overactive in overweight and obese individuals, sending out a signal that prompts people to eat more. 

Researchers wondered whether a drug that halted this action might curb appetite, and in 2001, the first animal study was conducted at the National Institute of Alcohol Abuse and Alcoholism in Bethesda, Md.

In the study, genetically altered mice that lacked cannabinoid receptors ate less than their litter mates, even after 18 hours of fasting. When the normal mice were given rimonabant, which blocked their CB1 receptors, the mice reduced their food intake.

In 2002, Sanofi-Synthelabo began human tests.

Acomplia works by selectively targeting and blocking the CB1 receptors, helping normalize the over-activation of the EC system and making hunger or cigarette pangs more manageable.

Much of the excitement about Acomplia stems from early results suggesting that the blocking of signals that control cravings not only facilitates weight loss, but that it also improves cardiovascular/ metabolic risk factors in overweight/obese patients.

In the RIO-Lipids trial, weight loss was accompanied by a decrease in waist size of 3.4 inches demonstrating a significant reduction in abdominal obesity, an independent marker for heart disease.

Dramatic improvements also were reported in lipid profile with a 23% increase in HDL-cholesterol (good cholesterol) and a 15% decrease in triglycerides.

Improvements in glucose tolerance and insulin levels were also reported. Approximately half of the patients diagnosed at the start of the study with metabolic syndrome, who received the higher 20 mg daily dose of Acomplia, no longer had this condition at the conclusion of the trial.

For those interested in a detailed description of the approved use of the diet drug Acomplia (rimonabant) in Europe, the Summary of Product Characteristics (SPC) approved by the EMEA can be read by clicking here.