Marijuana use in US doubled in a decade, says study

Marijuana use in the US more than doubled between 2001 and 2013 - from 4.5 to nearly 10 per cent, according to new research.

Laws and attitudes about marijuana are changing, with 23 states having medical marijuana laws and four of these states having also legalised marijuana for recreational use, researchers said.

Bridget F Grant of the National Institute on Alcohol Abuse and Alcoholism, and coauthors used nationally representative data on past-year prevalence rates of marijuana use, marijuana use disorder and marijuana use disorder among marijuana users in the US.

The prevalence of past-year marijuana use climbed to 9.5 per cent of adults in 2012-2013 from 4.1 per cent in 2001-2002, with increases particularly notable among women and individuals who were black, Hispanic, living in the South, middle-aged or older, the authors said.

The prevalence of a diagnosis of a past-year marijuana use disorder (abuse or dependence) also increased to 2.9 per cent in 2012-2013 from 1.5 per cent in 2001-2002, which means nearly 3 of every 10 Americans who used marijuana in the past year had a diagnosis of a marijuana use disorder (approximately 6.8 million Americans).

Groups with notable increases included individuals ages 45 to 64 and those individuals who were black or Hispanic, with the lowest incomes or living in the South.