Originally Published: 07 NOV 22 11:00 ET

Updated: 17 NOV 22 08:15 ET

By Jacqueline Howard, CNN

(CNN) -- Although the prevalence of e-cigarette use among teens has declined in recent years, those who do vape are starting younger and they're using e-cigarettes more intensely, a new study suggests.

Among adolescents who only use e-cigarettes, the percentage who used the products within the first five minutes of waking up in a day was less than 1% between the years 2014 and 2017, but that shifted to 10.3% from 2017 through 2021, according to the study published Monday in the medical journal JAMA Network Open.

"This increase in intensity may reflect increasing use of nicotine for self-medication in response to increases in adolescent depression, anxiety, tic disorders, and suicidality that occurred during the COVID-19 pandemic," the researchers -- from San Francisco and Massachusetts General Hospital -- wrote in the study.

"The pandemic has also been a lost year for school-based prevention and treatment efforts, meaning that abatement plans will need to be intensified to address the nicotine addiction in those adolescents who missed a year of contact with adults who might have otherwise helped them get treatment."

The researchers analyzed self-reported data from the US Centers for Disease Control and Prevention's National Youth Tobacco Surveys and Youth Risk Behavior Surveillance System. The data included a total of 151,573 survey respondents, all in middle or high school in the United States.

The data showed that, between 2014 and 2021, the age at which adolescents first started using e-cigarettes decreased and the intensity of their use increased -- rising from using e-cigarettes about nine or fewer days a month to 10 or more days a month.

The researchers found that the average age at first use got younger over time, by about 1.9 months per calendar year, for e-cigarettes but remained stable for other tobacco products. The mean age of survey respondents was 14.5 years old.

Among adolescents who currently use any type of tobacco product, the proportion whose first-ever use of a product at a young age was an e-cigarette increased from 27.2% in 2014 to 78.3% in 2019, and remained at 77% in 2021, according to the data.

'Concerning' trends in the intensity of use

The overall prevalence of e-cigarette use peaked in 2019 and then declined. But by 2019, more e-cigarette users were using within the first five minutes of waking up each day compared with traditional cigarette users.

"The changes detected in this survey study may reflect the higher levels of nicotine delivery and addiction liability of modern e-cigarettes that use protonated nicotine to make nicotine easier to inhale," the researchers wrote.

"The increasing intensity of use of modern e-cigarettes highlights the clinical need to address youth addiction to these new high-nicotine products over the course of many clinical encounters. In addition, stronger regulation, including comprehensive bans on the sale of flavored tobacco products, should be implemented."

This study's findings suggest that e-cigarettes may be putting a new generation of adolescents at risk for nicotine addiction, and research has shown that many adolescents are unaware that most e-cigarettes contain nicotine, said Ashley Merianos, a research affiliate member of Cincinnati Children's Hospital Medical Center and the Thirdhand Smoke Research Consortium, who was not involved in the new study.

"It is encouraging that the prevalence of e-cigarette use has declined among U.S. adolescents from 2019 to 2021. However, the addiction and intensity of use trends reported in this study are concerning, especially since tobacco use is typically established during adolescence," Merianos, who is also a faculty researcher at the University of Cincinnati, said in an email.

"Unfortunately, early nicotine addiction could overturn the significant tobacco control progress made over many decades," she said. "Currently, cigarette smoking is at a record low among U.S. adolescents, but the continued initiation and use of e-cigarettes among adolescents could halt this progress."

In 2020, the US Food and Drug Administration banned flavored cartridge-based e-cigarettes, other than tobacco or menthol, from the market. But the researchers noted in their study that after the ban, disposable flavored e-cigarettes rapidly gained popularity among adolescents, and they are calling for clinicians to be on alert for possible cases of nicotine addiction among young people.

"Because tobacco addiction is a chronic disease, clinicians should be ready to address youth addiction to these new high-nicotine products during the course of many clinical encounters," the researchers wrote in their study. "The increasing intensity of use of modern e-cigarettes highlights the need for local, state, and federal comprehensive bans on the sale of flavored tobacco products and consideration of ending the sale of these products on the open retail market, as has been done in 47 countries as of 2021."

Concern over 'more severe nicotine addiction'

The new study is among the first to examine nicotine use among adolescents during the Covid-19 pandemic, said Dr. Scott Hadland, chief of adolescent and young adult medicine at Mass General for Children and Harvard Medical School, who was not involved in the new research.

"Most of us pediatricians haven't been certain about what to expect with regard to teen nicotine use amid these upheavals -- but had been worried. This study fills a big knowledge gap," Hadland said in an email.

"National data suggest that adolescent vaping may have declined during the Covid pandemic -- we suspect because substance use often occurs when teens are among their peers, and Covid socially isolated many teens," he said. "But in my clinic, I have been seeing that the teens that 'do' vape are showing more severe nicotine addiction now than in all my years of practice."

Hadland added that the new study findings match what he has seen on the front lines in his own practice, including the earlier age at which youth start to use e-cigarettes, higher frequency of use, and greater symptoms of addiction, such as vaping first thing in the morning.

"Teens who vape often receive high levels of nicotine consistently throughout the day, which leads to greater nicotine dependence and risk for addiction. As a result, I routinely see teens who experience uncomfortable nicotine withdrawal if they try to stop vaping, as well as strong cravings to use," Hadland said in the email.

"I increasingly have needed to use medications (e.g., varenicline pills, nicotine patches, and nicotine gum or lozanges—and often a combination of these) to manage withdrawal symptoms and cravings in teens to help them quit," he said. "This is all a phenomenon of recent years."