Marijuana use rose this year among eighth, 10th, and 12th graders, and is now more common than cigarette smoking with high school seniors, a government survey found.

Daily marijuana use among seniors climbed to 6.1 percent in 2010 from 5.2 percent in 2009, sophomore use increased to 3.3 percent from 2.8 percent, and eighth-grade use reached 1.2 percent from 1 percent, according to the poll from the National Institutes of Health.

Efforts to legalize marijuana for medical purposes have sent "mixed messages" to youths and made it harder for parents to discourage drug use, said Gil Kerlikowske, director of the separate White House Office of National Drug Control Policy.

"Calling smoked marijuana 'medicine' is absolutely incorrect and it sends a terrible message," he told reporters Tuesday in Washington. "We know that the earlier someone starts, the greater difficulties they are going to have."

In January, New Jersey became the 14th state to legalize medical marijuana; Arizona followed last month.

The survey found that more than 21 percent of 12th graders reported smoking marijuana in the previous 30 days, while 19 percent said they had smoked cigarettes.

"Marijuana use during the teen and pre-teen years, when the brain continues to develop, places our young people at particular risk," Nora Volkow, head of NIH's National Institute on Drug Abuse, said in a statement.

The survey, conducted for the NIDA by the University of Michigan, questioned 46,482 students from 396 public and private schools this year.

It found that alcohol use among 12th graders dropped to the lowest level since the study began in 1975. The percentage saying they had consumed alcohol in the last year dropped more than 2 percentage points to 41 percent. Binge drinking among 12th graders dropped 2 percentage points to 23 percent.

But the survey also found "a significant increase" in the use of the psychoactive stimulant ecstasy, with 2.4 percent of eighth graders reporting taking the drug in the last year, up from 1.3 percent. Use among 10th graders rose to 4.7 percent from 3.7 percent.

And reductions in cigarette smoking stalled in all three grades after "several years of marked improvement on most measures," the NIDA said.