A new study has revealed that medical marijuana laws do not lead to increased use of the drug by teenagers.

Although pot smoking by teens is on rise, the new study suggested that medical marijuana laws are not the reason behind it.

The study looked at self-reported use of pot among more than one million adolescents from 48 US states from 1991 to 2014.

It was led by Prof. Deborah Hasin of the Mailman School of Public Health, at New York City's Columbia University and was published in the journal Lancet Psychiatry.

The researchers examined nearly a quarter-century's worth of data from a nationally administered survey American teenagers complete in Grades 8, 10 and 12. Their dataset included information provided by 1,098,270 adolescents.

During the time studied, 21 of the 48 states that administered the survey passed medical marijuana laws.

The researchers compared teen marijuana use in states with and without legislation. They also looked closely at usage rates in states with medical marijuana laws in the periods before and after the legislation went into effect.

The researchers found that there was no statistically significant increase in marijuana usage rates among Grade 10 and Grade 12 students after medical marijuana laws were put in place. It was also found that pit use dropped among Grade 8 students after legislation was adopted.

Hasin said, "Our findings provide the strongest evidence to date that marijuana use by teenagers does not increase after a state legalizes medical marijuana".

Benedikt Fischer, a senior scientist at the University of Toronto's Centre for Addiction and Mental Health said that this was the highest-quality study which answered the question that was lingering for some time.