An advisory panel to the Food and Drug Administration (FDA) in the U.S. have unanimously voted that the federal agency should refuse approval for a new weight loss drug.
The drug Zimulti (rimonabant) is made by French manufacturer Sanofi-Aventis and is already available in 18 other countries under the name Acomplia.
The advisory panel has rejected the drug on the basis that too many questions remain unanswered regarding the drug's potential side effects.
Trials of the drug showed that patients given the once-daily tablet reported twice as many psychiatric side effects, including depression, anxiety and sleep problems, than those who received a placebo.
Sanofi-Aventis had suggested that patients be screened for depression before they are prescribed the drug and also be reassessed by their doctors five times during the first year of treatment to avoid any potential problems.
As a rule the FDA follows panel recommendations and Sanofi has promised to address the committee's concerns.
Zimulti is one of a new breed of drugs that helps people shed pounds by blocking food craving signals in the brain and was developed by targeting the receptors that trigger intense hunger experienced after marijuana use.
In Sanofi-Aventis studies, Zimulti along with a reduced-calorie diet helped patients lose 5 percent more weight than diet alone over a one year period; patients who took the drug lost an average of 14.2 pounds, while others who got a placebo dropped about 3.5 pounds.
Sanofi said Zimulti also reduced waist size and improved levels of "good" cholesterol, blood sugar and blood fats called triglycerides.
But according to the FDA advisory panel, data showed Zimulti patients were twice as likely to have suicidal thoughts or mental problems such as depression and anxiety.
The panel were also very concerned that the drug's effect on the body could lead to an array of psychiatric symptoms, including anxiety, phobias, and post-traumatic stress disorders.
The FDA's medical officer Amy Egan says because of the potential market for the drug and the uncertainty about its risks, they are concerned about use in the general population.
Sanofi believes the risks to be manageable and say there is no evidence Zimulti caused suicidal thoughts or actions; but the FDA begs to differ.
The FDA previously refused to approve the drug to help smokers quit.
There are currently two FDA-approved prescription drugs for the long-term treatment of obesity: Meridia, an appetite suppressant, and Xenical, which limits the amount of fat the body can absorb.
Meanwhile, Alli, a lower-dose version of Xenical that does not require a prescription, goes on sale this week.