In medical marijuana states, not a lot has changed with teen use.  The availability of medical marijuana does not cause a surge in pot smoking among teens, according to a national, school-based survey.

When the survey results were aggregated across grade (grade 8 through 12) they found that the risk of marijuana use did not significantly change after the state passed a medical marijuana law. That is to say, adjusted prevalence for combined grades was 16.25% before the law passed, and 15.45% after the law passed (Adj. odds ratio 0.92, 95% CI 0.82-1.04, P=0.185).

In states that allowed the use of medical marijuana use among teens in grades 8 through 12, 15.87% of teens were using marijuana versus 13.27% in states where its use was barred (Adj. OR 1.27, 95% CI 1.07-1.51, P=0.0057), Deborah S. Hasin, PhD, of Columbia University’s Mailman School of Public Health, and colleagues reported in The Lancet Psychiatry.

“Hasin and colleagues postulated, as many would, that the passage of medical marijuana laws would increase adolescent marijuana use by contributing to the declining perception of the potential harms of marijuana,” Kevin P. Hill, MD, MHS, of Harvard’s McLean Hospital in Boston, wrote in an editorial in The Lancet Psychiatry. “Their well designed, methodologically sound study showed that this was not the case.“

“This study draws attention to the importance of undertaking rigorous scientific research to test hypotheses and using the results to develop sensible health policies,” Hill added. “Policies might sometimes be shaped by preconceived notions that do not end up being true, and Hasin and colleagues’ study is an example of such an occurrence.“

“[T]he growing body of research that includes this study suggests that medical marijuana laws do not increase adolescent use, and future decisions that states make about whether or not to enact medical marijuana laws should be at least partly guided by this evidence,” Hill wrote.

Hasin’s team looked at 24 years of survey data from the Monitoring the Future study, which included 1,098,270 adolescents who lived in the 48 contiguous states and attended more than 400 schools from 1991 to 2014. The teens were surveyed during eighth grade, the 10th grade, and the 12th grade.

In 23 states and the District of Columbia, some form of medical marijuana is permitted. And data were collected from 21 of those states.

Adjustments were made for individual-level factors like age, gender, race/ethnicity, socioeconomic status, and parental education; school-level factors like school size, public versus private, and urban/suburban versus rural location; and state-level factors like higher male or white population, and proportion of those over 25 who did not have a high school education.

The primary outcome of the survey was any marijuana use in the past 30 days. Hasin’s group also looked at marijuana use in the past 12 months, and teen exposure to changes in state-level medical marijuana laws.

The researchers looked at the data in terms of the overall passage of laws by 2014, and then year-by-year from 1991 through 2014. To account for variations in state laws, they classified states in one of three categories: no medical marijuana laws, medical marijuana laws that did not permit dispensaries, and medical marijuana laws permitting dispensaries.

For all grades combined, those states where medical marijuana was in some way legal, 15.87% of adolescents had consumed marijuana in the past 30 days, compared with 13.27% of those in states with no medical marijuana permissions (Adj. OR 1.27, 95% CI 1.07-1.51, P=0.0057).

Broken down by grade, the greatest disparity was seen among those teens in the 12th grade, as 22.36% of those in states with medical marijuana had used marijuana in the past month compared with 17.83% of those in non-medical marijuana states (Adj. OR 1.35, 95% CI 1.11-1.63, P=0.0024).

Slighter variations were found among 8th graders, 7.22% in legal states versus 6.95% in non-legal states, and among 10th graders, 18.02% in legal states and 15.04% in non-legal states.

Hasin’s group saw a potential confounder as the landscape prior to the changes in the law. “This effect, aggregated across years before and after passage of marijuana laws, suggests that, overall, states with a medical marijuana law had an increased prevalence of marijuana use even before the law was passed,” the authors wrote.

In their discussion, Hasin and colleagues mentioned one surprising finding: a post-law decrease in marijuana use among 8th graders, which they suggested could stem from growing up with a medical marijuana law — a cultural factor that might have lowered the likelihood of adolescents seeing marijuana as recreational, or, they wrote, the passage of the law could have prompted “parental vigilance and counter-efforts” against its use.

Study limitations included a lack of accountability for variations in state laws, such as amounts permitted, or approved illnesses, self-reported data bias, and some of the states included in the analysis had only recently passed medical marijuana legislation.

This study did not address the impact of legalized recreational marijuana.

Source: MedPage Today