Merck's development of taranabant, a diet drug which has been described as a competitor for Acomplia (rimonabant), must be going pretty well because the pharmaceutical giant has brought back top marketeer Len Tacconi to serve as the drug's global brand leader.

While taranabant, a cannabinoid-1 (CB-1) receptor inverse agonist that has a mechanism of action similar to that of Sanofi-Aventis' rimonabant, is still in Phase III trials, it now appears that the Merck drug may well beat Acomplia to the U.S. market.

Merck continues to say little about taranabant, but Sanofi-Aventis withdrew its application to market Acomplia in the U.S. in June after an FDA advisory panel recommended against approving it due to concerns over psychiatric side effects.

Merck has said it intends to file for FDA approval of taranabant in 2008, and Sanofi -- which continues to market rimonabant in Europe and some other countries -- now is not expected to refile for the U.S.before the Merck filing.

Tacconi, who left Merck less than a year ago to become president of Discovery Health, spent a decade with Merck orchestrating high-spending consumer marketing campaigns for drugs that included Singulair, Zocor and Vioxx.

Before joining Merck, Tacconi had led North American marketing for Weight Watchers.

Pfizer is working on what has been called a cannabinoid receptor antagonist, called CP-945598, which also is in Phase III trials, but has not indicated when it hopes to file for FDA approval.

What has never been made totally clear is whether the Pfizer drug is a receptor antagonist, which would operate differently than the Sanofi and Merck drugs. Some researchers have expressed the belief that a true CB-1 antagonist could possible help in suppressing appetite while minimizing undesirable side-effects.