Depressed? Merck's research neuroscientists would have reason to be. The pharma giant bet a fortune over the past decade that a novel compound that blocks a neurotransmitter called "Substance P" would become an effective new treatment for depression-a multibillion-dollar global market profitably dominated by Prozac, Paxil, and Zoloft. Merck bet wrong. Its aspiring antidepressant performed well in early experiments but flunked the phase III clinical trials required by the U.S. Food and Drug Administration. Not good.

Over the course of the multimillion-dollar tests and trials, however, researchers outside Merck observed a curious digestive detail signaling medical potential. The scientists noticed that ailing lab ferrets-yes, ferrets; they're the new rats-ingesting the Substance P blocker vomited much less than expected. Ferret vomit thus became the leading indicator that Merck's new compound enjoyed an unexpected effect on the brain. The drug apparently blocked neuroreceptors located in regions associated with both emotion and nausea-failing on the emotional front but helping curtail vomiting.