The Food and Drug Administration, in a harsh warning letter Monday, criticized Juul Labs for illegally marketing its e-cigarettes as less harmful than regular cigarettes and ordered the company to correct the violations immediately or face tougher enforcement actions.

The agency said it acted after reviewing testimony from a recent investigation by a House Oversight and Reform subcommittee into Juul’s marketing and promotion practices. The economic and consumer policy panel, in July hearings, accused Juul of “deploying a sophisticated program” to target children and teenagers, including at schools and summer camps, as part of an effort to become the nation’s largest seller of e-cigarettes.

The FDA’s warning letter said the testimony showed that Juul marketed its vaping products as “modified risk tobacco products” — meaning the company included claims that the products “present a lower risk of tobacco-related disease or are less harmful than one or more other commercially marketed tobacco products.“

Under federal regulations, such “modified-risk claims” must be authorized by the FDA. Juul’s failure to get such authorization, the FDA said, means that the company sold and marketed “adulterated” products.

The FDA noted the testimony at the congressional hearing indicated that a Juul representative, speaking at a school, said Juul “was much safer than cigarettes” and that the “FDA would approve it any day.” The panel’s investigation — based on about 55,000 documents — was detailed in a hearing and a memo compiled by subcommittee staff members. Juul officials who testified said they had ended the school programs and that the company no longer sold many types of e-flavored cigarettes in retail stores.

A Juul spokesman said the company “will fully cooperate” with the FDA.

The FDA action comes as federal health authorities investigate five deaths from a mysterious lung illness tied to vaping. There are now 450 possible cases in 33 states and one territory, including five deaths, they said.

Although officials said the definitive cause of the illnesses remains unknown, “the severity of the illness and the recent increase in the incidence of this clinical syndrome indicates that these cases represent a new or newly recognized and worrisome cluster of pulmonary disease related to vaping,” according to a report by health officials in Wisconsin and Illinois. A large number of the victims seem to have used marijuana products, though a small number said they used nicotine vapes. Many of the samples contain vitamin E acetate that experts said could cause lung injury.

The FDA, in a second letter sent to Kevin Burns, Juul chief executive officer, on Monday, asked the company for documents and information about several marketing and outreach practices detailed in the July congressional hearing. It said that despite Juul’s commitment to address the surge in youth use, the company’s products continue to represent “a significant proportion” of the overall use of e-cigarette products by children. “Some of this youth use appears to have been a direct result of JUUL’s product design and promotional activities and outreach efforts,” the FDA said.

The FDA is also raising questions about Juul’s “Make the Switch” campaign, which the agency worries presents Juul as “a safer alternative to cigarettes” — despite the fact that the FDA has not authorized such a message.

In addition, the agency asked Juul to explain why it uses nicotine-salt e-liquids and a high concentration of nicotine in its Juul pods, which officials said could increase the products’ addictiveness.

The agency wants answers to those questions within 30 days.

The FDA, in the letter to Burns, also said that in April 2018 it had asked the company for documents relating to marketing practices and research into marketing, effects of product design, public health impact and adverse experiences. But it said the company apparently provided Congress more documents than it gave the FDA.

In a statement, acting FDA commissioner Norman “Ned” Sharpless said “companies must demonstrate with scientific evidence that their specific product does in fact pose less risk or is less harmful” than conventional cigarettes. “JUUL has ignored the law, and very concerningly, has made some of these statements in school to our nation’s youth,” he said.

The FDA on Monday gave the company 15 working days to respond to the warning letter, and demanded a description of corrective actions and a plan for maintaining compliance with the law. The inability to ensure compliance “may result in the FDA initiating further action, including, but not limited to, civil money penalties, seizure, and/or injunction,” the agency said.

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