“The agency has dedicated significant resources to review products from the companies that account for most of the US market,” Califf said in the statement. “We recognize these make up a significant part of the available products and many have played a disproportionate role in the rise in youth vaping.”

Juul’s application lacked sufficient evidence to show that allowing its products to be sold in the US would be appropriate for the protection of public health, the FDA said. Some of the company’s study findings “raised concerns due to insufficient and conflicting data,” the agency said in its statement.

Read more: Juul users who fear FDA ban are rushing to hoard e-cigarettes

Once a richly valued startup, Juul has seen its fortunes decline in recent years after regulators cracked down on flavored e-cigarette products and lawsuits accused the company of marketing to underage users. The company has said that it never targeted youth in its advertising.

Shares of Altria Group Inc., which holds a 35% stake in the company were up 1.2% in New York trading on Thursday. The stock had slumped on Wednesday after the Wall Street Journal reported that the FDA was expected to reject Juul’s application for clearance.

Regulators had hoped e-cigarettes would help adults to quit smoking, which is a major cause of premature death. However, the FDA, which has received thousands of applications for approval from e-cigarette companies, has allowed only a few to stay on the market.