Nearly 23 percent of U.S. teens smoked pot in the last month ANN ARBOR, Mich., Dec. 21 (UPI) -- More than 6 percent of U.S. high school seniors say they smoked marijuana daily, up from 5.1 percent five years ago, a survey says. This year's Monitoring the Future survey, an annual survey of eighth, 10th and 12th-graders conducted by researchers at the University of Michigan, also found nearly 23 percent said they smoked it in the month prior to the survey. Thirty-six percent said they smoked within the previous year. For 10th graders, 3.5 percent said they used marijuana daily, with 17 percent reporting past month use and 28 percent reported use in the past year. The use escalated after eighth grade, when only 1.1 percent reported daily use, and 6.5 percent reported past month use. More than 11 percent of eighth graders said they used marijuana in the past year, the survey said. The survey also showed teens' perception of marijuana's harmfulness was down. Forty-two percent of eighth graders said occasional use of marijuana was harmful; while 67 percent said regular use as harmful -- the lowest since the survey began tracking risk perception for this age group in 1991.