Legalising marijuana use has had no impact on the number of teenagers getting high, new research in Colorado has found.
The state voted to legalise the drug for users 21 and over in 2012, and the first retail stores opened last year.
A Colorado Department of Public Health and Environment survey of 17,000 high school students in 2011 found 22 percent of them had used marijuana in the past 30 days. A repeat of the survey conducted at the end of last year, with the results released today, shows little has changed -- with 21.2 percent admitting to using marijuana.
"The survey shows marijuana use has not increased since legalisation, with four of five high school students continuing to say they don't use marijuana, even occasionally," the department said.
While still illegal in most parts of the United States, surveys show around 21.7 percent of high school students use marijuana at least once a month -- about the same as in Colorado.
"These statistics clearly debunk the theory that making marijuana legal for adults will result in more teen use," said Mason Tvert, spokesperson for the Marijuana Policy Project, which backs legalising and regulating marijuana just like alcohol.
Colorado has since been followed by Alaska, Oregon and Washington in legalising recreational marijuana, but is the only state so far to have retail shops.