The US regulators on Tuesday declined to approve the experimental weight loss drug Contrave, requesting for a clinical trial to further assess its heart risks.
The surprise announcement sent Orexigen stock plunging and came after an FDA advisory panel had in December recommended the approval of the drug, the first anti-obesity pill in more than a decade.
The stock dove 72 percent in early trading, losing 6.57 points to 2.50 dollars at 1430 GMT.
The FDA voiced concern about heart safety in patients, the company said.
"Specifically, the letter stated that 'before your application can be approved, you must conduct a randomized, double-blind, placebo-controlled trial of sufficient size and duration to demonstrate that the risk of major adverse cardiovascular events in overweight and obese subjects treated with naltrexone/bupropion does not adversely affect the drug's benefit-risk profile,'" the company statement said.
"We are surprised and extremely disappointed with the Agency's request in light of the extensive discussion and resulting vote on this topic at the December 7 Advisory Committee meeting," said Michael Narachi, president and CEO of Orexigen.
"We plan to work closely with the Agency to gain more information to determine the appropriate next steps regarding the Contrave application."
The FDA expert panel said in December that the drug was only modestly effective and was found to cause slight boosts in blood pressure and pulse.
It recommended approval in a 13-7 vote and also urged a wider trial to assess potential heart attack risks. The FDA does not have to follow the panel recommendations but it often does.
The FDA last year acted on the panel's recommendations and denied two new obesity drugs, Qnexa and Lorcaserin, over cancer and heart risks.
About one third of Americans are obese, and the only FDA-approved prescription diet pill on the market is Switzerland-based Roche Holding AG's Xenical, which was approved by the FDA in 1999.