(CBS) - With medical marijuana approved in more states each year and recreational use legalized in Colorado and Washington, experts are concerned that more teens may use the drug because they believe it's safe.
A Feb. 25 study published in the International Journal of Drug Policy found that about 10 percent of high school students who would otherwise be at a low risk for picking up a pot-smoking habit -- which includes those who don't smoke cigarettes, students with strong religious beliefs and those with non-marijuana smoking friends -- say they would use marijuana if it was legal.
For high school seniors alone, the shift would make up a 5.6 percent absolute increase in lifetime pot use prevalence. About 45.6 percent of high school seniors admitted to smoking pot in the study, meaning that legalization would increase that number to 51.2 percent.
The data was pulled from the Monitoring the Future survey, which was a nationally-representative survey of students in the eighth, 10th and 12th grade. The students were polled from 2007 to 2011, before recreational marijuana use was legalized in Colorado and Washington following the November 2012 elections.
The effects from more high school students admitting to being okay with using pot if it was legal could extend throughout their lives, according to the study's authors.
"Lifetime prevalence increases as adolescents age into adulthood. So by age 26, 64 percent of young adults in the U.S. are expected to use marijuana in their lifetime in the current policy context. We don't know whether those found to be at risk in this study are the same adolescents that are going to use at an older age regardless of legal status," Dr. Joseph J. Palamar, assistant professor at the department of population health at NYU Langone Medical Center, said in a press release.
The Partnership at Drugfree.org reported in a 2012 study that frequent marijuana use was increasing among teens. Almost 10 percent of teens surveyed said they smoked pot at least 20 times a month.
The increase may not just be limited to young people. A September 2013 study by the Substance Abuse and Mental Health Services Administration (SAMHSA) that surveyed 70,000 Americans 12 and older in 2012 showed that the rate of marijuana and heroin use had increased over the past few years. About 7.3 percent of Americans said they smoked pot in that year.
Dr. Stephen Ross, director of addiction psychiatry at NYU Tisch Hospital in New York, told CBS News chief medical correspondent Dr. Jon LaPook that he was worried because trends until a few years ago had been showing a decline in teen marijuana use. As more states legalized pot, more people said they didn't think there was a risk in using, and marijuana use has increased in the last few years.
More health news: Morning Rounds with Dr. LaPook
"We know that in high school students, perception of harm is very much correlated with use. If high school students think something is harmful they're much less likely to use it, and the converse is very much the case," Ross explained to LaPook, who is also a professor at NYU Langone Medical Center.
Ross said that about 10 percent of people who try marijuana get addicted. Though this risk is lower than the one out of three tobacco users who will get hooked or the 15 percent of drinkers who will become alcoholics, there is still a chance that people can become dependent on marijuana to the point where it interferes with their daily lives.
Ross points out that there's also the false impression that marijuana doesn't cause harm. Research has shown that weed may affect the developing brain. An August 2012 study showed that smoking marijuana frequently as a teen could lead to drop in IQ as an adult. However, other studies have refuted that claim.
Some studies also suggest that pot may be linked to memory problems and a higher schizophrenia risk for some adolescents.
Ross said currently there's no evidence that long-term use of marijuana causes brain damage or functional impairment once you stop, unlike alcohol. That doesn't mean that it isn't a possibility.
"We really don't know. We need more research to understand how harmful marijuana is in the future," he said.
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