A lot of people had given up on neuropeptide Y antagonists as potential obesity therapies, but Merck kept the faith. They were enrolling patients in a combination trial with one of their compounds (MK-0557, a Y5 ligand which I believe is this guy) as recently as three years ago, although I believe that all clinical work stopped on the drug sometime in 2005. (See the note on this site from New Zealand; a search within the page for "0557" will turn it up).

Now the post-mortem for the drug has appeared in Cell Metabolism. Nature's news site has a good summary of the story, although they treat it as more of a fresh news bulletin than it really is. In short, the compound can cause statistically significant (but very modest and clinically useless) weight loss.

It joins a large and varied junk heap of obesity compounds (this category has comments on some of them). I'm surprised that Merck was still cranking away on this particular mechanism, but they have a reputation for tenacity. And they also have several other compounds in the clinic, including another CB-1 antagonist as competition for rimonabant. Speaking of which, where is rimonabant? And will it avoid being the largest compound on the same heap?