The Food and Drug Administration on Thursday ordered Juul to stop selling e-cigarettes on the U.S. market, a profoundly damaging blow to a once-popular company whose brand was blamed for the teenage vaping crisis.

The order affects all of Juul’s products on the U.S. market, the overwhelming source of the company’s sales. Juul’s sleek vaping cartridges and sweet-flavored pods helped usher in an era of alternative nicotine products that were exceptionally attractive to young people. The company’s initial dominance invited intense scrutiny from antismoking groups and regulators who feared the products would do more harm to young people than good to cigarette smokers trying to quit.

Although teenage vaping rates have declined during the coronavirus pandemic, public health experts and lawmakers continue to express concerns about the additive nicotine in some e-cigarettes that remain on the market, including brands like Puff Bar, whose fruity flavors appeal to young people.

The F.D.A.’s decision did not deal with Juul’s relationship to youth vaping. Instead it was based on what the agency said was insufficient and conflicting data from the company about potentially harmful chemicals that could leach out of Juul’s e-liquid pods. There was not an imminent health threat to consumers, the F.D.A. said, but it did not have enough evidence to assess the potential risks.

“Today’s action is further progress on the F.D.A.’s commitment to ensuring that all e-cigarette and electronic nicotine delivery system products currently being marketed to consumers meet our public health standards,” Dr. Robert M. Califf, the agency commissioner, said in a statement. And he acknowledged that many of the e-cigarette products had played a role in the rise in teenage vaping.

The move by the F.D.A. is part of a wide-ranging effort to remake the rules for smoking and vaping products and to reduce illnesses and deaths caused by inhalable products containing highly addictive nicotine.

On Tuesday, the agency announced plans to slash nicotine levels in traditional cigarettes as a way to discourage use of the most deadly of legal consumer products. In April, the F.D.A. said it would move toward a ban on menthol-flavored cigarettes.

The F.D.A.’s action against Juul in particular is part of a newer regulatory mission for the agency, which must determine which electronic cigarettes currently for sale, or proposed for sale, will be allowed to permanently remain on shelves. It has already granted permission for other companies’ e-cigarettes to stay on the market.

But it could take years before some of the agency’s new initiatives take effect — if they can withstand fierce resistance from the powerful tobacco lobby, antiregulatory groups and the vaping industry.

Juul said it disagreed with the F.D.A.’s findings and planned to appeal. The company could seek a stay from the agency or from a court pending an appeal to the F.D.A. The company has not said which path it will seek but it will try to keep its products on the market during any proceedings.

“We intend to seek a stay,” Juul’s statement concluded, “and are exploring all of our options under the F.D.A.’s regulations and the law, including appealing the decision and engaging with our regulator.”

Public health groups hailed the ruling.

“The F.D.A.’s decision to remove all Juul products from the marketplace is both most welcomed and long overdue,” said Erika Sward, national assistant vice president of advocacy for the American Lung Association. “Juul’s campaign to target and hook kids on tobacco has gone on for far too long.”

A statement from the American Vapor Manufacturers Association, an industry trade group, hinted at the fight ahead.

“Measured in lives lost and potential destroyed, F.D.A.’s staggering indifference to ordinary Americans and their right to switch to the vastly safer alternative of vaping will surely rank as one of the greatest episodes of regulatory malpractice in American history,” Amanda Wheeler, the association’s president, said in a statement.

Broadly, the F.D.A. is walking a fine line in remaking the landscape for nicotine products. It is trying to wean the public off traditional cigarettes while permitting less harmful vaping products that do not attract a new generation of users: The new devices must be appealing for smoking cessation but not so appealing that they lure young people en masse.

The agency’s ruling against Juul capped a nearly two-year review of data that the company had submitted to try to win authorization to continue selling its tobacco and menthol-flavored products in the United States. Specifically, Juul sought approval for — and the F.D.A. rejected — a Juul vaping device and four different pods, including tobacco pods with nicotine concentrations of 3 percent and 5 percent and menthol-flavored pods with the same levels.

“It’s clear that the company was given an opportunity to address questions and concerns related to safety, toxicology and potential genotoxicity, and for whatever reason the company was unable to meet its burden and that led to a negative marketing order,” said Mitch Zeller, a former director of the agency’s tobacco center who retired in April.

He said Juul could submit an entirely new application for a revamped product — one that presumably addressed the agency’s concerns about the leaching of chemicals.

The F.D.A. began an investigation into Juul’s marketing efforts four years ago. Before that time, Juul had advertised its product using attractive young models and flavors like cool cucumber and creme brulee that critics said attracted underage users.

In April 2018, the F.D.A. announced a crackdown on the sale of such products, including Juul’s, to people under the age of 21.

Use among young people had soared. In 2017, 19 percent of 12th graders, 16 percent of 10th graders and 8 percent of eighth graders reported vaping nicotine in the previous year, according to Monitoring the Future, an annual survey done for the National Institute on Drug Abuse.

For its part, Juul routinely denied that it targeted young people, but it was pursued in lawsuits and by state attorneys general, with some cases resulting in millions of dollars in damages against the company. In one settlement in 2021, Juul agreed to pay $40 million to North Carolina, which represented various parties in the state who asserted the company had helped lure underage users to vaping. More than a dozen other states have lawsuits and investigations that are still pending.

The news is somewhat less weighty for the industry now than it would have been in Juul’s heyday, given the company’s plummeting market share. Once the dominant player with 75 percent of the market, Juul now has a considerably smaller share of the market.

But the news delivers a significant blow to Altria, formerly known as Philip Morris and the maker of Marlboro, which in December 2018 bought 35 percent of Juul for $12.8 billion.

Altria made the investment to counteract slowing tobacco sales, while Juul looked to Altria as an ally to help it navigate increased regulatory scrutiny.

Neither of those strategies appear to have worked out.

Altria has written down the value of its investment in Juul by more than $11 billion, to $1.7 billion. Altria, which gets about 90 percent of its revenue from smokable products, saw revenue fall slightly last year. Its stock is down more than 40 percent over the past five years, and 20 percent just in the past month. Juul, for its part, saw its revenue fall to $1.3 billion in 2021, from $2 billion in 2019, with about 95 percent in U.S. sales.

“We are disappointed with today’s decision and continue to believe that e-vapor can play an important role in harm reduction for adult smokers,” Altria said in a statement.

At its peak, Juul had more than 4,000 employees. It now has slightly over 1,000, mostly in the United States, but with some in Canada, Britain and other countries.

E-cigarettes have been sold on the U.S. market for more than a decade without formal F.D.A. authorization, because they did not fall under the agency’s regulatory purview for several years.

In 2019, the F.D.A. issued a warning letter to Juul, saying that the company violated federal regulations because it had not received approval to promote and sell its products as a healthier option to smoking.

The F.D.A. recently said it had so far rejected more than a million applications for products it considered more of a health risk than a benefit. In October, it authorized R.J. Reynolds to continue marketing Vuse. This was the first time the agency granted approval to a vaping product made by a big cigarette company

In March, the agency authorized several tobacco-flavored products from Logic Technology Development, saying the company was able to show that its products were likely to help adults make the transition from traditional cigarettes while posing a low risk of attracting young, new users.

Some tobacco control experts said the decision to ban Juul from the U.S. market could be counterproductive.

Clifford Douglas, director of the University of Michigan Tobacco Research Network, said that many experts had come to see Juul and other e-cigarettes as valuable tools for helping adult smokers quit conventional cigarettes.

“They are off ramps that can provide smokers an alternative to combustibles, which are responsible for virtually every death related to tobacco,” he said. “But now that off ramp is being narrowed and sort of paved over, which is putting millions of adult lives at stake. One hopes Juul can respond effectively to the request for more scientific analysis, make any product adjustments that may be called for, and again offer their products to adults in need.”

Lauren Hirsch, Christina Jewett and Sheila Kaplan contributed reporting.