Yet another weight loss drug that works in a manner similar to diet pill Acomplia (rimonabant) -- this one being developed by a partnership of Solvay Pharmaceuticals of Belgium and Bristol-Myers Squibb -- is advancing in clinical trials, according to an announcement Dec. 8th.

Solvay said it had begun a Phase IIb trial of SLV319, a CB1-antagonist which like Acomplia works by blocking cannabinoids receptors in the brain, following encouraging results in earlier stage Phase II trials.

Solvay said the start of the Phase IIb trial of SLV319 triggered a milestone payment of $25 million from its partner Bristol-Myers Squibb.

The announcement by Solvay followed reports in the past 10 days that weight-loss drugs based on CB1-antagonists under development by pharmaceutical giants Pfizer and Merck have now moved into Phase III trials.

Eli Lilly & Co. is also believed to have a diet drug based on a CB1-antagonist under development.

Despite the fact that Acomplia remains stalled at the U.S. Food and Drug Administration with Sanofi expressing hope for a decision on approval by the end of April, it now appears possible that within a few years there may be as many as four of five of these diet drugs on the market.