More teens also are getting high on prescription pain pills and attention-deficit drugs, according to eighth, 10th and 12th graders surveyed by the University of Michigan for the National Institute on Drug Abuse.
The increase of teens smoking pot is partly because the national debate over medical use of marijuana can make the drug's use seem safer to teenagers, researchers said. In addition to marijuana, fewer teens also view prescription drugs and Ecstasy as dangerous, which often means more could use those drugs in the future, said White House drug czar Gil Kerlikowske.
The "continued erosion in youth attitudes and behavior toward substance abuse should give pause to all parents and policy-makers," Kerlikowske said.
"These latest data confirm that we must redouble our efforts to implement a comprehensive, evidence-based approach to preventing and treating drug use," Kerlikowske, the director of the Office of National Drug Control Policy, said in remarks prepared for his Monday speech at the National Press Club in Washington.
Marijuana use, while well off peak levels of the late 1990s, has edged up. According to the study of 47,097 students, among this year's 12th graders, 20.6 percent said they used it within the past month, compared with 19.4 percent in 2008 and 18.3 percent in 2006.
Among 10th graders, pot use in the past month rose to 15.9 percent this year from 13.8 percent in 2008.
"The upward trending of the past two or three years stands in stark contrast to the steady decline that preceded it for nearly a decade," said Lloyd Johnston, who has directed the annual survey since it started in 1975.
The percentage of eighth-graders who saw a "great risk" in occasionally smoking marijuana fell from 50.5 percent in 2004 to 48.1 percent in 2008 and 44.8 percent this year. The perceived danger of using Ecstasy once or twice fell among eighth graders, from 42.5 percent in 2004 to 26 percent in 2009.
"When the perception of the danger goes down, in the following years you see an increase in use," said National Institute on Drug Abuse Director Nora Volkow.
Volkow said teens falsely reason it's less dangerous to get high on prescription drugs "because they're endorsed by the medical community." But she said prescription narcotics like OxyContin and Vicodin are highly addictive and can act as gateways to heroin, a cheaper high.
Use rates of both prescription narcotics rose among this year's 10th graders, with 8.1 percent saying they had used Vicodin in the past year compared with 6.7 percent of the same grade in 2008. For OxyContin, the figure rose to 5.1 percent from 3.6 percent.
Recreational use of the attention-deficit drug Ritalin was lower than five years ago. But the attention-deficit drug Adderall, appearing for this first time in this year's survey, showed use rates similar to those for Ritalin at its peak, which for 12th graders was around 5 percent.
By all measures, alcohol remained the most widely used illicit substance among teens, with 43.5 percent of 12th graders reporting taking a drink in the past month. That's a little change from last year, but down from 52.7 percent in 1997 - a year that showed high percentages of substance abuse. All three grades reported drops in binge drinking for 2004-2009.
Cigarette use patterns showed a continuation of the dramatic drop from a decade ago. In 1997, 19.4 percent of eighth graders reported smoking within a month. That fell to 6.8 percent last year and 6.5 percent this year. The rate for 12th graders dropped from 36.5 percent in 1997 to 20.1 percent this year.
"There's not going to be much further improvement unless policies change," such as higher taxes to discourage kids on a budget and further limits on public smoking, Johnston said.
Only 2.4 percent of this year's 12th graders said they'd ever used methamphetamine, down from 2.8 percent in 2008 and 8.2 percent in 1999.