A research analyst who has been one of the biggest boosters of Sanofi and diet drug Acomplia (rimonabant) has sent a note to investors saying Sanofi has gone silent to most investors, analysts and the media, and will remain quiet until it announces quarterly financial results on Oct. 31.

This decision not to let anyone know what is going on -- particularly what is happening with Acomplia at the Food and Drug Administration, where the diet drug seems stalled for reasons that have never been disclosed -- gives Sanofi's shareholders "plenty of reason to be nervous," Forbes magazine reported on October 5th.

U.S. approval of rimonabant, Forbes notes, has been delayed for seven months and counting.

One issue Sanofi has barely addressed, Forbes correctly observes, is why?

Even Gbola Amusa, a research analyst at Sanford C. Bernstein who has been a big booster of rimonabant, now seems frustrated at Sanofi's failure to address such key issues, and told Forbes "it's clear there's a difference between the way they communicate, compared to other companies."

Sanofi said a couple of months ago that it expected to bring rimonabant to the U.S. market -- presumably under the name Zimulti -- in the second half of 2006, but most analysts think it now is extremely unlikely that the FDA will act on Acomplia this year.

Forbes notes that the drug, which works by turning off brain receptors, also seems to cause psychiatric side effects: a subset of patients quit taking their medicine because of anxiety or depression.

"Neurological side effects seem the most likely reason for the long delay," Forbes reports, "and they could conceivably prevent Acomplia from joining the ranks of blockbuster drugs like Plavix and Lipitor."