Over 22 million of US adults smoke marijuana and their number has risen sharply during the past decade, according to the results of a government study. Almost a third of the users show signs of addiction, officials say.
Almost one in ten adult Americans smokes marijuana, which is more than double compared to the early 2000s, according to the findings published in the journal JAMA Psychiatry on Wednesday.
The jump reflects a cultural shift on the drug, researchers say.
The study compared a health survey from 2001-02 to a similar analysis in 2012-13, showing that a number of marijuana users has grown from 4.1 to 9.5 percent.
This increase was "particularly notable among women and individuals who were black, Hispanic, living in the South, middle-aged or older," the study says.
'There are risks'
At the same time, about three in ten users were "meeting the criteria for addiction," according to the director of the National Institute on Alcohol Abuse and Alcoholism George Koob.
The signs of abuse and dependence may include smoking more often than intended, unsuccessful efforts to cut down, missing out on obligations due to marijuana use, and a buildup of tolerance or symptoms of withdrawal, according to the researchers.
"Given these increases, it is important that the scientific community convey information to the public about the potential harms," Koob added.
More research is needed on the causes of problematic use, said study's lead author and Columbia University professor Deborah Hasin.
The results "show people can use marijuana without harms, but there are risks," she said.
The use among teenagers is even higher, other surveys report.
Majority backs legalization
Some 58 percent of Americans supports legalization of marijuana, according to a separate Gallup poll released on Wednesday.
Only the age group of 65 and older remains opposed to it, results say.
Cannabis use has been legalized in Alaska, Colorado, Oregon and Washington, with many other US states considering the move. In addition, 23 US states now allow medical marijuana.
dj/bw (AP, AFP)