Scientists uncover how weight-loss drugs work

Weight-loss drugs such as fen-phen and Meridia deliver a two-pronged punch to curb appetite, researchers have found.

This class ofdrugs enhances the effect of the brain chemical serotonin, but until now, scientists didn't know how.

Dr. Joel Elmquist, professor of internal medicine at the University of Texas Southwestern Medical Center, and his colleagues discoveredserotonin activates some neurons to curb appetite while at the same blocking other neurons that normally act to boost appetite.

The study appears in Thursday's issue of the journal Neuron.

"The finding increases the understanding of the molecular circuitry that controls body weight in response to changing levels of serotonin," said Elmquist. "An overarching goal of this understanding, for humans, is to design specific, safe drugs to fight obesity."

It's been nearly a decade sincefen-phen, a combination offenfluramine and phentermine, was pulled from the market after some people developed heart complications.

Meridia isapproved as a weight-losstreatment in Canada. The U.S. consumer group Public Citizen haslobbied for it to be removed from the market, saying it is linked to 29 deaths, and increasesthe risk ofcardiovascular problems. The drug's manufacturer saysit is safe to use if taken as directed.

The researchersdiscovered the dual approach by tracing the effect of this class of drugson the feeding behaviour of normal and genetically engineered lean and obese mice.

Serotonin has to regulate both types of neurons to promote weight loss, the researchers said.