Marijuana use among U.S. college students rose 22 percent over the past decade, according to a study released this week by the Harvard School of Public Health. And "very competitive" colleges in the Northeast posted the largest increases.

Last year, 15.7 percent of students surveyed claimed to have used marijuana in the past month. In 1993, the rate was 12.9 percent.

"These new findings should be a source of concern for those involved with the prevention and treatment of illicit drug use among young people," Lecturer on Social Psychology Henry Wechsler, one of the authors of the report, said in a press release.

Wechsler is also director of the College Alcohol Study, a School of Public Health study whose first report was released six years ago and of which the marijuana study is a part.

The authors of the report say the study's results may mark the end of a 20-year decline in drug use.

"This trend threatens to slow or reverse the decline in illicit drug use among adults in the United States since 1980," the report reads.

But prevention cannot begin at the university level.

"[We] need education programs for younger students as well as programs in college," Weschler wrote in an e-mail message. "The younger one begins to use drugs, alcohol or tobacco, the greater the problems."