Updated

A decade-long decline in teens' use of pot has stalled and some teen attitudes on how harmful marijuana can be may be softening, according to a federal survey on teen drug use released Monday.

The findings were based on a survey of roughly 47,000 eighth, 10th and 12th-graders conducted by the University of Michigan for the National Institute on Drug Abuse.

Marijuana use across the three grades showed a consistent downward trend starting in the late 1990s. But the decline has since stopped, and use rates for the three grades showed a slight uptick between 2007 and 2009, from about 12.9 percent to about 14.3 percent, lead researcher Lloyd Johnston said Monday night.

The national debate over medical use of marijuana could be making the drugs 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 them in the future, said White House drug czar Gil Kerlikowske.

"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.

In the 2009 survey, reported past-year marijuana use was 32.8 percent of 12th graders, 26.7 percent of 10th graders and 11.8 percent of eighth graders, generally not much changed from 2008.

Marijuana was at its recent peak in 1997, when 17.7 percent of eighth-grade students, 34.8 percent of 10th-grade students and 38.5 percent of 12th-grade reported using the drug at least once within a year of being interviewed.

Students were asked how much people risk harming themselves if they smoke marijuana occasionally or smoke marijuana regularly. Fewer eighth-grade students said that people who smoked pot put themselves at great risk than a year ago.

"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.

A group backing legalization of marijuana said the figures show the futility of trying to ban pot, rather than regulate its use.

"Clearly, regulation of tobacco products has worked to curb access by teens, and it's time to apply those same sensible policies to marijuana," said Bruce Mirken, spokesman for the Washington-based Marijuana Policy Project.

The survey also found that in the past five years, a drop in methamphetamine use in the past year was found among all three grades.

From 2004 to 2009, alcohol use across the three grades also dropped. 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 the same period 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 from 2004 to 2009.

Cigarette use continued its 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, said Johnston.

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On the Net:

Monitoring the Future: http://www.monitoringthefuture.com

National Institute on Drug Abuse: http://www.nida.nih.gov