The troubled path of diet drugs continues to look challenging, especially after a U.S. Food and Drug Administration (FDA) panel recommended Thursday that the agency not approve a new anti-obesity medication—the second of three to come up for evaluation this year.

The new drug, called lorcaserin, acts on the brain's serotonin, a neurotransmitter involved in appetite, digestion, memory, mood and other functions. Serotonin also plays a role in the cardiovascular system, and the diet drug fen-phen (fenfluramine and phentermine) was pulled from the market in the 1990s after it was linked to heart valve problems. When given in high doses, the new medication also gave many rats tumors (though human trials have not been linked to increase cancer risk). "In my opinion the potential risks of the medication outweigh the potential benefits," Heidi Connolly, a panel member and professor of medicine at the Mayo Clinic, told Bloomberg News.

Other committee members, however, pointed more to a questionable level of efficacy than concerns over safety in their final vote, which was nine to five against approval. "I really didn't have a lot of issues with the risk," Eric Felner, a panel member and pediatric endocrinologist at Emory University, told The New York Times. "I just didn't see it as being that efficacious."

The FDA requires new diet drugs to help people lose at least five percent more of their body weight than a placebo. Those on the lorcaserin lost about 3.3 percent more weight than those on the placebo, according to the Times. But the drug did meet another FDA criteria that at least twice as many people taking the medication (versus those on a placebo) lose five percent or more of their weight.

Qnexa, another diet drug, was voted down by the committee in July. And the panel is slated to assess the drug Contrave—the last of the three new possible treatments—in December, the Times reports. Although the FDA is not required to follow the suggestions of the advisory panel, it often acts on its decisions. The company that makes lorcaserin, Arena Pharmaceuticals, will continue to pursue FDA approval, Arena CEO Jack Lief told Bloomberg, and the agency's decision is anticipated to come in October.

Many observers of the diet drug field remain skeptical that a pharmaceutical panacea for the growing obesity epidemic will emerge anytime soon—despite widespread obesity and big incentives to develop a blockbuster drug. Another possible setback for the field: Meridia (sibutramine), a drug that is already on the market, might be pulled from shelves in the U.S. as it already has been in Europe. Its use has been linked to stroke and heart attacks in those who already have elevated risks, and the FDA panel was split (eight to eight) in a September 15 vote as to whether to stop its sale.

Image courtesy of iStockphoto/FotografiaBasica