Nearly 10 percent of U.S. teens - about 1.5 million - smoked marijuana heavily, some 20 times, in the past month, a new survey shows.

The Partnership at Drugfree.org and MetLife Foundation found that past-month marijuana use – particularly heavy use – has increased 80 percent among U.S. high school students since 2008.

This marks an upward trend in teen marijuana use over the past three years. Past-month use was 27 percent in 2011 (up from 19 percent in 2008), which translates to about 4 million teens. The last time marijuana use was as widespread among teens was in 1998 when past month use was also 27 percent.

"These findings are deeply disturbing as the increases we're seeing in heavy, regular marijuana use among high school students can spell real trouble for these teens later on," said Steve Pasierb, president and CEO of The Partnership at Drugfree.org.

Teens now report seeing more of their peers smoking marijuana and only 26 percent agree with the statement, "in my school, most teens don't smoke marijuana" (down from 37 percent in 2008). Also, 71 percent of teens say they have friends who use marijuana regularly (up from 64 percent in 2008).

Read the report at Drugfree.org.