Legalising the medical use of cannabis has not led to a surge in the numbers of adolescents using it in the USA, according to new research that surprised its authors and will encourage those hoping for relaxation of the law elsewhere. Since 1996, 23 US states and the District of Columbia (DC) have approved the medicinal use of cannabis. In the states of Colorado, Washington, Alaska and Oregon and DC, recreational use is also legal. These moves towards permissiveness, even where possession of the drug is restricted to medical use, have caused many critics to worry that cannabis use would rise, especially among teenagers. That assumption was the starting point for the research carried out by Dr Deborah Hasin, professor of epidemiology at Columbia University Medical Center in New York, and her colleagues. However, the findings from 24 years of data from more than one million adolescents in the 48 contiguous states did not substantiate those fears. Their paper in the journal Lancet Psychiatry says that the use of cannabis by adolescents was already higher in the states that have opted for medical legalisation. But the change in the law did not lead to a jump in numbers.
Analysing data from a national study called Monitoring the Future, which collects information from 50,000 pupils aged 13 to 18 in the 8th, 10th and 12th grade (years 9, 11 and 13 in Britain) every year, they found there had not been a rise even after taking into account individual, school and state-level factors that can affect marijuana use (such as age, ethnicity, public or private school and proportion of each state’s population that was male or white). “Our findings provide the strongest evidence to date that marijuana use by teenagers does not increase after a state legalises medical marijuana,” said Dr Hasin. “Rather, up to now, in the states that passed medical marijuana laws, adolescent marijuana use was already higher than in other states.”