The University of Michigan's Institute for Social Research has been monitoring drug use among teens for 36 years. This year's "Monitoring the Future" study had responses from more than 46,000 8th, 10th, and 12th graders.
They found that marijuana use is on the rise. 43.8% of 12th graders said they've used marijuana in their lifetime. That's up from 42% in 2009, and 42.6% in 2008. From the study:
Marijuana use, which had been rising among teens for the past two years, continues to rise again this year—a sharp contrast to the considerable decline of the preceding decade
Alcohol use, on the other had has been decreasing. 54.1% of 12th graders said they'd been drunk in their lifetime. That's down from 56.5% in 2009, and 54.7% in 2008. From the study:
Alcohol use—and, specifically, occasions of heavy drinking—continues its long-term decline among teens into 2010, reaching historically low levels.