A nationwide study in the United States has found no evidence that legalising the use of marijuana for medical purposes leads to increased use among teenagers.
The study, published in The Lancet Psychiatry Journal showed no significant difference in adolescent marijuana use in 21 states with medical marijuana laws before or after implementation of these laws.
In the study, Dr Deborah Hasin, Professor of Epidemiology at Columbia University Medical Centre and colleagues examined the relationship between the legalisation of medical marijuana and adolescent marijuana use by looking at survey data from over a million students aged 13-18, between 1991 and 2014.
Since 1996, 23 US states and the district of Columbia have passed laws allowing the medical use of marijuana, and state legalisation has raised concerns that teenagers will find the drug more accessible and acceptable.
The findings showed that although marijuana use was more prevalent in states with medical marijuana laws than others, the rates of adolescent use did not increase following legalisation.
According to Dr Hasin, "Our findings provide the strongest evidence to date that marijuana use by teenagers does not increase after a state legalises medical marijuana.
"Rather, up to now, in the states that passed medical marijuana laws, adolescent marijuana use was already higher than in other states.
"Because early adolescent use of marijuana can lead to many long-term harmful outcomes, identifying the factors that actually play a role in adolescent use should be a high research priority."
The research is being presented at the College on Problems of Drug Dependence annual meeting in Phoenix, Arizona and was funded by the US National Institute on Drug Abuse, Columbia University Mailman School of Public Health, and the New York State Psychiatric Institute.
In February 2015, President Obama discussed the marijuana legalisation sweeping the US, and said it was his "suspicion that you're gonna see other states looking at this."
He said: "The position of my administration has been that we still have federal laws that classify marijuana as an illegal substance, but we’re not going to spend a lot of resources trying to turn back decisions that have been made at the state level on this issue.
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