Teen perception changed after legalisation of marijuana?

A new study has found that the use of marijuana increased and the drug's perceived harmfulness decreased among teenagers in Washington after it was legalised for recreational use by adults.

The findings, published online by JAMA Pediatrics, indicated that in Washington among eighth and 10th-graders, perceived harmfulness declined by 14.2 percent and 16.1 percent, respectively, while marijuana use increased two percent and 4.1 percent, respectively.

Among states that did not legalise recreational marijuana use, perceived harmfulness decreased 4.9 percent and 7.2 percent among eighth and 10th-graders, respectively, and marijuana use decreased by 1.3 percent and 0.9 percent, respectively.

Magdalena Cerda from the University of California Davis School of Medicine, Sacramento and co-authors examined the association between legalising recreational use of marijuana for adults in the two states and changes in perception of harmfulness and self-reported adolescent marijuana use before and after legalisation.

Washington and Colorado became the first two states to legalise recreational use of marijuana for adults in 2012.

The researchers used data from nearly 254,000 students in the eighth, 10th and 12th grades.

They compared changes prior to recreational marijuana legalisation (2010-2012) with post-legalisation (2013-2015) and with trends in other states that did not legalise recreational marijuana.

The authors offered several potential explanations for increase in marijuana use among eighth and 10th graders in Washington including that legalisation may have increased availability through third-party purchases.

"Although further data will be needed to definitively address the question of whether legalising marijuana use for recreational purposes among adults influences adolescent use and these influences may differ across different legalisation models," the researchers explained.

"A cautious interpretation of the findings suggests investment in evidence-based adolescent substance use prevention programs in any additional states that may legalise recreational marijuana use," they added.