Diet drug rimonabant (Acomplia / Zimulti) faces its moment of truth in the United States during the week ahead.

On Tuesday, June 12th, the FDA staff will for the first time reveal its views on the long-delayed diet drug.

The following day, June 13th, the agency's Endocrinologic and Metabolic Drug Advisory Committee, a panel of outside experts, will air various concerns about Acomplia and its side-effects, and vote on whether to recommend FDA approval.

While the FDA does not have to follow the recommendations of its advisory committees, it generally does -- and the combination of the staff report and the advisory panel vote should strongly signal what to expect in July when the regulatory agency's decision on approval of rimonabant is now due.

In a best case scenario for the developer of rimonabant, Sanofi-Aventis, Zimulti -- as it will be known in the United States -- could be on the market by early fall.

In a worst case scenario (well, not the absolute worst), the FDA could ask for more trial data keeping Zimulti off the U.S. market and leaving it to be sold as Acomplia in Europe, much of the rest of the world, and by mail-order for another couple of years.

If history is any guide, the FDA's release of its review of rimonabant will identify issues that have concerned regulators since Sanofi-Aventis first sought approval of rimonabant in the United States two years ago.

Sanofi during this time has provided very few hints of what was holding up action at the FDA.

But it long has been apparent that the FDA's questions for the most part do not involve the effectiveness this novel obesity treatment, which works by blocking the CB1 receptor in the brain, but center on the neuropsychiatric side-effects reported during the Acomplia clinical trials.

Not only were worrisome instances of anxiety, depression and nausea experienced by a number of participants in the trials, but concern also has been voiced over the high drop-out rate from the trials among participants getting the dose of Acomplia submitted for approval to the FDA.

Sanofi-Aventis has consistently downplayed concern over rimonabant's side effects, and has said it will be "pleased to have the opportunity to present its data on rimonabant and to exchange with experts" at Wednesday's advisory committee meeting.

But with the FDA freshly focused on safety concerns as a result of the recent furor over whether regulators were slow in getting out safety data on a GlaxoSmithKline diabetes drug, Sanofi and its hopes for rimonabant may well be in for a rocky week.