In the latest sign that things are going will with Merck's development of a competitor to diet drug Acomplia (rimonabant), the pharmaceutical giant is bringing back Len Tacconi to serve as global brand leader for its weight-loss drug taranabant.

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.

While Merck continues to say little about the Phase III trials of taranabant, a cannabinoid-1 (CB-1) receptor inverse agonist that has a mechanism of action similar to that of Sanofi-Aventis' rimonabant, the company has said it plans to seek FDA approval for taranabant next year.

Sanofi-Aventis withdrew its application to market Acomplia in the United States in June after an FDA advisory panel recommended against approving it due to concerns over psychiatric side effects. Sanofi is not expected to refile with the FDA before the Merck filing.

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, in fact, a receptor antagonist, which would operate differently than the Sanofi and Merck drugs, or whether it is like rimonabant and taranabant also an inverse agonist.

Receptor antagonists and inverse agonists bind to the same receptors, but produce different effects.

While an inverse agonist like rimonabant or taranabant in binding to CB-1 receptors has exactly the opposite effect of the THC in cannabis, which gives people the munchies and induces mild euphoria, an antagonist when it binds to the receptor might produce a different result.

Some researchers have expressed the belief that a true CB-1 antagonist could possible help in suppressing appetite while minimizing undesirable side-effects (like depression) on CB-1 inverse agonists.