The Food and Drug Administration seized "thousands of pages of documents" in a surprise inspection of e-cigarette maker Juul's San Francisco headquarters last week, the agency said Tuesday.
The FDA is looking into the company's marketing practices as Commissioner Scott Gottlieb calls teen use of nicotine vaping devices an "epidemic."
It builds on the agency's request in April for company materials related to how Juul products appeal to kids. The most recent inspection, conducted Friday, "sought further documentation related to Juul's sales and marketing practices, among other things," the FDA said in a statement.
Juul CEO Kevin Burns said the company walked the FDA through "every part" of its business, including its marketing practices and age-verification tools used on its online shop.
"It was a constructive and transparent dialogue," Burns said in a statement.
Juul, which controls about 73 percent of the market, has been at the center of the FDA's attention this year as e-cigarette use soars among teens.
The inspection comes weeks after the FDA announced a crackdown that requires e-cig manufacturers, including Juul, to submit plans to address youth use of their products within 60 days. The agency also threatened to ban some flavored nicotine liquids, which critics say attract kids to e-cigarettes.
Over the past year, the number of high school students who have used e-cigarettes in the past 30 days has skyrocketed by about 75 percent, preliminary data from the Centers for Disease Control and Prevention's annual National Youth Tobacco Survey show, according to people familiar with the data. They asked not to be identified because the report isn't yet public.
That means roughly 3 million, or about 20 percent of high school kids, are using e-cigarettes, up from 1.73 million, or 11.7 percent, in last year's National Youth Tobacco Survey. The complete data set is expected to be published later this year.
The e-cigarette craze has driven what's arguably the largest uptick of teen nicotine use in decades. That follows years of cigarette smoking among teens dropping to record lows.
Gottlieb, the FDA commissioner, said he believes in e-cigarettes' potential to help the 37.8 million adult smokers quit cigarettes. That includes a role for flavors.
"I think people should interpret the fact that I and others have made such a dramatic shift from our prior position with respect to these products as representing the fact that we have seen information that is deeply disturbing and startling in terms of the rapid rise of youth use over a short period of time," Gottlieb told CNBC in a September interview.