More teens are regularly using marijuana by vaping rather than smoking, even as mysterious lung illness claims young lives across the United States, according to a study released Wednesday.

Fourteen percent of high school seniors said they vaped marijuana in the previous month, according to the National Institutes of Health's annual Monitoring the Future survey. That's nearly double the rate from 2018, the second-largest annual increase recorded in the survey's 45-year history. It's also up dramatically from 4.9% in 2017.

The survey, conducted earlier this year, also found that 22% of high school seniors — about the same percentage as in 2018 — say they use marijuana, which can be smoked, vaped or eaten through an edible.

"It appears that kids are switching how they are using marijuana, not how much they are using marijuana," said Ken Warner, an emeritus professor of health policy at the University of Michigan, who was not affiliated with the study.

About 26% of high school seniors said they vaped nicotine within the previous month, mirroring results from a separate survey published by the Centers for Disease Control and Prevention earlier this year. Meantime, less than 6% of 12th graders said they smoked conventional cigarettes, according to the new survey, which was funded by the NIH's National Institute on Drug Abuse.

The survey of more than 42,000 students in grades 8, 10 and 12 was conducted by Richard Miech and colleagues at the University of Michigan.

"We've seen [increases] in the past among the three grades, never at this size that we're observing with vaping," said Dr. Nora Volkow, director of the National Institute on Drug Abuse. "Never."

The study shows how popular vaping is becoming, especially among young people. Newer products have transformed centuries-old methods of consuming nicotine and THC, the compound that products a high in marijuana. They can be used discreetly and are often available in sweet flavors that make vaping more palatable and critics say helps attract teens.

A surge in teen vaping during the past few years has sent lawmakers and regulators scrambling. President Donald Trump and top U.S. health officials have been weighing for months whether to ban flavored e-cigarettes in a bid to make the products less appealing to kids.

An outbreak of a deadly lung disease among people who vape revealed another critical health risk: People are vaping unregulated and sometimes deadly THC oils. The illness has hospitalized 2,409 people across the country and killed 52, the CDC said last week. Health officials have tallied 152 different THC products that patients reported using. A majority of the patients are young men.

"Teenagers are believing less and less there's any harm in marijuana, and then on top of that you have sleek, cool devices that actually have become very, very popular among teenagers," Volkow said. She also noted that vaping allows people to consume potent doses of THC without the pungent smell that smoking marijuana produces.

Volkow anticipates the lung illness outbreak may deter some teens from vaping THC. She thinks stories of otherwise healthy teenagers ending up in intensive care may cause teens to "think twice."

While the study shows increases in vaping, it also identifies a significant decrease in teen cigarette smoking. In 2019, less than 6% of high school students reported smoking in the past month, down from 20% in 2009, according to the survey.

"The data are just tremendously encouraging on cigarettes," Warner said. "That's the most deadly use we're talking about."