US marijuana legalisation has not led to rise in use by adolescents, study finds

Data on one million teenagers shows marijuana use did not increase in US states where it was legalised, with fall among youngest children, authors of study find

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.