Orexigen Therapeutics Inc. says U.S. health officials have declined to approve the experimental weight loss pill Contrave and want the company to conduct an additional study.

The Food and Drug Administration request suggests the agency may yet approve the drug, which analysts have viewed as the most promising of three new diet pills recently submitted to the agency. But the FDA has asked for an additional study to address potential heart safety issues.

Orexigen said it is disappointed with the FDA’s decision and will work with the agency to determine its next step.

Contrave is a combination pill, mixing an antidepressant with an anti-addiction drug to curb appetite.