A growing number of U.S. teenagers are vaping marijuana -- a habit that in some ways may be more risky than old-fashioned pot smoking, a new study finds. Researchers found that between 2017 and 2019, the percentage of teens who reported any marijuana use in the past month ticked upward slightly -- from 13.9% to 15.4%. What really changed, the study found, was how kids were using the drug. There ...