Detroit ? 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.

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.

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.