(Reuters) - The sleek Juul electronic cigarettes have become a phenomenon at U.S. high schools, vexing educators and drawing regulatory scrutiny over their sweet flavors and high nicotine content.

Electronic cigarette device made by JUUL is shown in this picture illustration taken September 14, 2018. REUTERS/Mike Blake/Illustration

Now, a new wave of lower-priced Juul knock-offs is showing up at convenience stores, vape shops and online - despite a U.S. Food and Drug Administration rule banning the sale of new e-cigarette products after August 2016 without regulatory approval.

Start-ups and major tobacco firms have launched more than a dozen new high-nicotine devices with Juul-like designs since the FDA imposed the deadline, according to a Reuters review of the companies’ online advertisements, social media posts and public statements.

An electronic cigarette device made by JUUL (R) is shown next to other similar devices (L to R) Vuse Alto, Suorin ishare and myblu in this photo illustration taken September 20, 2018. Picture taken September 20, 2018. REUTERS/Mike Blake/Illustration

The FDA earlier this month threatened to ban Juul and four other leading vaping products unless their makers take steps to prevent use by minors. But the warning came after companies introduced a slew of new Juul copycats following the August 2016 deadline with no regulatory consequences.

In a statement to Reuters, the agency said it was investigating whether certain brands are being improperly sold without FDA approval and that it “plans to take additional action on this front very soon.” The agency said it would focus on products with high-nicotine concentrations and flavors appearing to target young people, and take “swift action wherever appropriate.”

The FDA set the August 2016 deadline to rein in the fast-growing industry but allowed sales of Juul and other older devices to continue without regulatory approval until 2022.

The companies that started marketing new devices after the deadline include startup firms such as Kandypens, Myle Vapor and VGOD, as well as large multinational tobacco companies including British American Tobacco Plc and Imperial Brands Plc.

Kandypens touted its new Rubi vaping device last October - more than 14 months after the August 2016 cutoff - with an Instagram post saying it had been “working hard over here for the last 12 months” on the product. Vaping distributor VGOD posted on its website in May that it was “an honor to finally introduce the STIG,” referencing its Stig Pods, a disposable three-pack of high-nicotine devices.

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British American Tobacco chief executive Nicandro Durante said on a July 2018 earnings call that the company would be launching its higher-nicotine Vuse Alto product in the United States the following month. Imperial Brands announced its myblu brand of e-cigarettes in a February 2018 press release.

Kandypens, Myle and VGOD did not respond to requests for comment.

Spokespeople for Imperial Brands and British American Tobacco said their products were compliant and on the market before August 2016. Imperial Brands said it had purchased an existing e-cigarette brand and renamed it. British American Tobacco did not respond to questions about its marketing or sales.

A spokeswoman for Juul Labs Inc, Victoria Davis, said the company is cooperating with regulators and working to prevent underage use of a product designed to help adult smokers quit tobacco cigarettes.

“No minor or non-nicotine user should ever try Juul,” Davis said.

‘FROZEN MYSTERY POP’

E-cigarettes vaporize a liquid that contains nicotine, the addictive stimulant that gives smokers a rush. The Juul design mimics a flash drive - with plug-in cartridges of concentrated nicotine juice. It is far more compact than earlier vaping devices and produces less vapor, making it easy to use without being detected - an attribute some health advocates say attracts teenagers.

Juul’s imitators are also small and compatible with higher-nicotine blends, though some can also be filled with lower-strength juice.

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The Chinese company Suorin introduced several such devices to the United States over the past year. Many high-schoolers and college students said they have switched to these products because buying widely available nicotine liquids is less expensive than Juul pods.

Natalia Pena and Rizza Colon vape outside the shop they work at, Cloud99 Vapes, in Manhattan borough, New York, U.S. September 20, 2018. REUTERS/Melissa Fares

In a statement, Suorin said it didn’t have “clear guidance” from the FDA on regulations governing its newer products but hopes to better understand how to fully comply. The company said its products are only intended for adult smokers.

One Juul pod has the nicotine content of about 20 cigarettes – the number in a traditional pack – according to Juul’s marketing. A pod can be consumed in a day by a heavy user, according to interviews with Juul customers.

Many of the newest blends from Juul and its imitators - called “nicotine salts” in the industry - contain a compound called benzoic acid, which lowers the pH level of the liquid. That reduction allows users to take in more nicotine without a bitter taste, according to the U.S. Centers for Disease Control and Prevention (CDC).

In addition to the devices, dozens of high-nicotine e-liquids have arrived on the market with names such as “frozen mystery pop,” “rainbow drops” and “Tokyo chocolate banana,” which critics say are designed to attract young customers.

Vaping proponents argue the Juul and similar new products give cigarette smokers looking to quit a much better option than lower-nicotine e-cigarettes.

“It gives the same exact sensation as a cigarette, except you don’t wake up coughing at 2 a.m.,” said Charles Trejo, a manager at V for Vape, a Los Angeles retailer.

Adam Trubitt, 21, smokes a Juul vaporized cigarette in Washington Square Park, Manhattan, New York, U.S., August 30, 2018. Picture taken August 30, 2018. REUTERS/Shannon Stapleton

Public health researchers say high-nicotine vaping devices like the Juul have proven adept at drawing in new customers, including teenagers, who never used tobacco.

“What they’re doing is creating addicts in large numbers,” said Dr. Robert Jackler, a professor who heads a group studying the impact of tobacco advertising at Stanford University.

High-nicotine vaping devices amount to a “weaponization” of the drug, he said, citing research showing young people are particularly susceptible to nicotine addiction, which could lead them to other addictions including cigarettes.

HIGH SCHOOL ‘JUUL ROOMS’

“What they’re doing is creating addicts in large numbers." Dr. Robert Jackler, a professor who heads a group studying the impact of tobacco advertising at Stanford University

The companies launched the copycat devices as Juul’s market share surged from 13.6 percent of the e-cigarette market in early 2017 to more than 70 percent now, according to a Wells Fargo analysis of Nielsen retail data, which does not include online sales.

The FDA’s regulation of e-cigarettes has come under scrutiny in recent months as Juul’s popularity has taken off. Anti-smoking advocates complained about the Juul lookalikes in an August letter to the FDA, saying the agency had failed to assert its authority over companies that had “evaded the review process.” The FDA said it planned to respond to the letter but declined further comment.

Vaping increased by nearly eightfold between 2011 and 2017 among U.S. high school students, according to the most recent CDC data. Experts say last year’s survey likely underestimates the increase because it was conducted before a surge in Juul sales.

Many high schools have resorted to locking bathrooms – jokingly called “Juul rooms” by students. Marcella Bianco, who helps develop school anti-vaping curriculum for the non-profit organization Catch My Breath, said elementary schools have recently started requesting materials.

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Educators fear the high-nicotine devices could erode decades of progress in reducing youth tobacco use. Smoking among high school students declined from 15.8 percent to 7.6 percent between 2011 and 2017, according to the CDC, but e-cigarette use grew from 1.5 percent to 11.7 percent over the same period.

“It’s like a flashback to 20 years ago,” said Kathryn Hensley, a school board member in St. Lucie County, Fla. “Are we starting all over again?”

An electronic cigarette device made by JUUL is shown in this picture illustration taken September 14, 2018. REUTERS/Mike Blake/Illustration

E-cigarettes have occupied a regulatory gray area in the United States since they emerged a decade ago. Only in 2016 did the FDA finalize rules to regulate e-cigarettes, including the requirement that companies get approval for new products.

Research on the long-term health effects of e-cigarettes is limited. They are widely viewed as safer than tobacco cigarettes because they don’t contain the same cocktail of toxic and cancer-causing chemicals.

The U.K. Royal College of Physicians said in a 2016 report that e-cigarettes were 95 percent less harmful than smoking tobacco, citing a reduction in the risk of serious disease and death. The CDC has said e-cigarettes are safer than conventional cigarettes but has not assigned a specific risk reduction because the products can vary widely.

Some health experts are particularly worried about the impact of nicotine from e-cigarettes on adolescents. Research from a 2016 U.S. Surgeon General’s report found that such exposure could have “lasting adverse consequences for brain development and cognition” on teenagers. A study released by the National Academy of Sciences this year cited evidence that vaping among young people increases the risk of eventually smoking tobacco.

BANNED IN OTHER COUNTRIES

High-nicotine vaping devices and liquids are not allowed in many other parts of the world, including in the European Union and the United Kingdom, which have both set nicotine limits at 20 mg/mL in e-cigarette liquids. Regulators said that level was effective for most smokers trying to quit.

Juul pods are rated at 59 mg/mL, according to the company’s marketing. Israeli regulators last month banned Juul out of concern over its high nicotine content, saying the device “posed serious danger to public health.”

Davis, the Juul Labs spokeswoman, said in August the company was “incredibly disappointed” with what it called the Israeli government’s “misguided decision” to crack down on healthier alternatives to tobacco cigarettes.

Imperial Brands’ new myblu product arrived in the United States earlier this year. Matt Kessler, a spokesman for Fontem Ventures, the Imperial Brands unit that owns myblu, said the brand complies with the FDA rules because it is a re-imagination of a similar e-cigarette that was marketed by a company that Imperial brands acquired a year earlier.

The new myblu brand, however, offers 4 percent nicotine strength, meaning at least 40 mg/mL, according to company advertising, higher than any previously offered by the earlier e-cigarette model, called My Von Erl.

Devices that vaporize higher-nicotine liquids fall under the definition of new products subject to FDA review, according to the 2016 regulation. Kessler declined to comment further on nicotine levels in myblu, saying only that the product “is compliant with FDA regulations.”

Durante, the CEO of British American Tobacco, acknowledged on the July earnings call that its Vuse Alto device had not been widely available before the August 2016 deadline. He said that’s not required under FDA rules.

“To be grandfathered” by the FDA, he said, “you could be in market, in one store, two stores only in the whole country.”

The FDA declined to comment on whether myblu and Vuse Alto are compliant or if availability in one or two stores would be considered “on the market.” The agency said it would consider “the totality of the evidence” to decide a whether a vaping product had been commercially available before the regulatory deadline.

Rizza Colon works at the shop Cloud99 Vapes in Manhattan borough, New York, U.S. September 20, 2018. REUTERS/Melissa Fares

STRUGGLE TO QUIT

“Everybody either has one or is looking for one." - Milo Gringlas, a Cornell University freshman says the Juul is ubiquitous on campus

As new high-nicotine Juul competitors arrive, vaping enthusiasts on YouTube are posting reviews of the next “Juul killer” aiming to take a piece of the red-hot market.

Milo Gringlas, a freshman at Cornell University, said Juul has become so ubiquitous on campus that a popular late-night food truck now sells vaping devices and nicotine liquids.

“Everybody either has one or is looking for one,” he said.

Austin Tompkins, who lives in Los Angeles, has struggled for the last six months to kick his addiction to Juul, which he started using about three years ago, when he was 19. He realized he needed to stop when he would wake up in the middle of the night needing another hit.

In his latest attempt, he’s made it two months without vaping. The urge hasn’t gone away.

“I’m telling you, right now, I would love a hit of a Juul,” he said.