Heavy marijuana use by teenagers is up 80 percent since 2008, according to a national survey released by The Partnership at Drugfree.org and the MetLife Foundation.

Nearly 10 percent of U.S. teens -- about 1.5 million youth -- smoked marijuana heavily, some 20 times in the past month, according to the Partnership Attitude Tracking Study, sponsored by MetLife Foundation.

Other findings:

-Past-month use of marijuana is up 42 percent

-Past-year use of marijuana is up 26 percent

-Lifetime use of marijuana is up 21 percent, which translates to 8 million teens

The upward trend in marijuana use follows a ten year period (1998-2008) where marijuana use declined, said Steve Pasierb, president of The Partnership at Drugfree.org.

Marijuana use creates a "gateway attitude" that leads teens to try other drugs and change social behavior and circumstances, Pasierb said. "Ninety percent of all adult addicts started drug use in their teen years," he said.

According to the survey 26 percent of teens agree with the statement, "in my school , most teens don't smoke marijuana" and 71 percent of teens say they have friends who use marijuana regularly.

Pasierb said marijuana use among teens is often tolerated by parents who consider it a relatively benign alternative to the "harder stuff," like cocaine, methamphetamines, and heroin. That mentality needs to change, he said.

"Kids who learn at home (of the dangers of drug use) are half as likely to use," he said.

In California the proliferation of medical marijuana dispensaries may be a factor in the increase, Pasierb said. Medical dispensaries "need to make certain there is a medical reason" for marjiuana use before selling it to anyone, he said.

Parents should speak with their children and explain marijuana use as a "health issue," he said. Federal budget cuts to the Office of Safe and Drug-Free Schools have limited the exposure of anti-drug campaigns and drug and alcohol education resources in schools, he said.

The 23rd annual Partnership Attitude Tracking Study (PATS) surveyed 3,322 teens in grades 9-12 and 821 parents. The margin of error is plus or minus 3 percent for the teen sample and plus or minus 3.4 percent for the parent sample, according to the organization's press release.

Additional results include:

-Teen boys show an overall increase in marijuana use. Past-year use among teen boys is up 24 percent and past-month use among teen boys is up 38 percent.

-Half of Hispanic teens report they have used marijuana in the past year versus 40 percent for African Americans and 35 percent for Caucasians.

-Teen abuse of over-the-counter and prescription drugs has not increased. Among teens, past-year abuse of prescription pain relievers such as Vicodin and OxyContin has plateaued at about percent.

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