Beaten down from every angle in the past couple of months, Sanofi-Aventis (NYSE:SNY) got more downbeat news this week, when new potential safety issues arose for one of its most important compounds, Acomplia.

Acomplia is approved in the European Union as a weight-loss treatment. But as The Wall Street Journal and other news sources reported, this week a British health-care agency reported a number of new "psychiatric events," including suicide and suicide attempts, among patients taking the drug.

Acomplia logged sales of approximately $34 million in the most recent quarter. It was approved for marketing in 2006, and it was supposed to be the bright star in Sanofi's drug pipeline, making up for the declining sales of other top drugs facing generic competition.

But new potential safety issues keep cropping up for the compound, and some countries' health-care agencies, including Germany's, have been reluctant to pay for its use. Like Pfizer's (NYSE:PFE) Chantix, Acomplia was also developed as treatment to help patients stop smoking, although Sanofi has failed to persuade regulatory agencies that its benefits in this indication outweigh its risks.

Last year, the European Union tightened Acomplia's warning label, restricting its use in patients on antidepressants. No regulatory actions are pending as a result of these newfound incidents in the U.K., and it's important to remember that correlation does not necessarily imply causation.

The FDA has refused to approve Acomplia in the U.S., and in 2007, Sanofi gave up on a second attempt to get the drug past the agency. New safety incidences undoubtedly won't help it clear these U.S. regulatory hurdles.

Drugmakers who successfully gain approval for weight loss and anti-obesity drugs can reap billions of dollars in rewards, if their drugs' side effects are mild enough. Multiple drugmakers like Arena Pharmaceuticals (NASDAQ:ARNA) and Amylin Pharmaceuticals (NASDAQ:AMLN) have weight-loss compounds in their drug pipelines for exactly this reason.

It's important to remember that large pharmaceutical companies like Sanofi-Aventis face new setbacks with their compounds all the time. Even by the pharmaceutical industries' own standards, though, Sanofi has had more than its share of bad news in 2008. Its shares are down 22% since the beginning of the year as it copes with a tough business environment, some regulatory failures in its pipeline, and new generic competition threats. This new data won't sink Acomplia's near-term sales prospects, but every new report of a serious adverse event with Acomplia lowers its ultimate market potential. That's why this news casts such a dark cloud for Sanofi and its investors.