The U.S. Food and Drug Administration has placed highly anticipated diet drug rimonabant (Acomplia / Zimulti) on a slow track for review, and developer Sanofi-Aventis said it now hopes for an FDA decision on approval of the diet pill by April 26th.

A spokesperson for Sanofi acknowledged that the April date is only "an indication" based on the six months typically taken by the FDA for this type of review, and said: "Maybe it will take further time."

Sanofi also declined to say how quickly it expects to launch Acomplia in the United States -- probably under the name Zimulti -- even if the drug is approved by the FDA in April.

"We do not want to speculate on the launch date," the spokesperson added.

Sanofi, as usual, provided no clues in its terse statement entitled "Rimonabant Update in the United States" as to what information it provided to the FDA on Oct. 26, saying only that the FDA "considered its Oct. 26, 2006 resubmission to be a complete class 2 response to the FDA Feb. 17, 2006 action letter."

But while Sanofi had nothing further to say, speculation was rife among analysts that the regulatory agency's concerns are centered on Acomplia's side effects, particularly depression.

The encouraging results Sanofi reported for Acomplia in its SERENADE diabetes trial earlier this week were tempered by news that one person in 17 (5.8 percent) of those taking Acomplia suffered from what was termed "depressed mood," compared to one person in 143 in the group on a placebo.

The problem was serious enough for more than one-third of those suffering from depressed mood that they dropped out of the SERENADE study:

"We remain concerned about Acomplia's psychiatric profile, specifically regarding depression and anxiety," Bear Stearns analyst Alexandra Hauber said in a note to investment banking clients, adding that the FDA might well ask one of its independent panels of experts to weigh in on the drug.

The FDA panel that would consider Acomplia, the Endocrinologic and Metabolic Drugs Advisory Committee, has thus far not announced any plans to hold a public meeting on Acomplia in the first part of 2007.