According to researchers at UC Davis and Columbia University Mailman School of Public Health, marijuana consumption among 13-14-year olds and 15-16-year olds increased respectively by two percent and four percent in the state of Washington since the introduction of the 2015 law authorising recreational use of the drug.
The study also found that since legalisation negative perceptions of marijuana among Washington teenagers in the same age categories had declined by 14% and 16% respectively.
In the United States, nine states have now authorized the recreational use of marijuana, while while 26 have legalised it for medical purposes. Most recently California, Nevada, Maine and Massachusetts voted to change their laws in November 2016. They join Colorado, which legalized in 2012, Oregon, Alaska and the State of Washington, which legalized in 2015, as well as the US capital Washington DC, which legalised in 2014.
Worrying impact on teenagers
In concrete terms, anyone over the age of 21 can now legally procure one ounce of marijuana for recreational use. The law also allows for the cultivation of six marijuana plants, provided they are not on public view. Retail sales from licensed vendors are permitted and taxed at 15 percent.
"While legalisation for recreational purposes is currently limited to adults, potential impacts on adolescent marijuana use are of particular concern," points out Magdalena Cerdá, the author of the study which was published in Jama Pediatrics.
In view of the increasing number of states moving to legalise marijuana, the researchers argue that changes to the law should be accompanied by prevention programs that raise teenagers' awareness of the potential risks of marijuana.