New York, March 17 (IANS): The percentage of Americans having marijuana use disorder has nearly doubled between 2001-2013, reveals a new study.

The research also showed that 2.5 percent of adults -- nearly 6 million people -- experienced marijuana use disorder in the past year.

The data showed that marijuana use disorder is about twice as common among men than women.

Younger age groups are much more likely to experience the disorder than people aged 45 and over, and that those at the lowest income levels were at the highest risk, the findings showed.

The collaborative study was carried out by scientists at Columbia University's Mailman School of Public Health, Columbia University Medical Center, and the National Institute on Alcohol Abuse and Alcoholism (NIAAA), part of the US National Institutes of Health.

The study also found that marijuana use disorder is often associated with other substance use disorders, behavioural problems, and disability, and goes largely untreated.

The data was collected in the 2012-2013 wave of NIAAA's National Epidemiologic Survey on Alcohol and Related Conditions (NESARC), the largest ever conducted on the co-occurrence of alcohol use, drug use, and related psychiatric conditions. 

For this study, over 36,000 US adults were interviewed about alcohol, drug, and related psychiatric conditions. 

"An increasing number of American adults do not perceive marijuana use as harmful," said study lead author Deborah Hasin, professor at Columbia University's Mailman School of Public Health.

"While some can use marijuana without harm, other users do experience negative consequences, which can include mental and physical problems, and impaired functioning. This paper helps provide information on some of those risks," Hasin noted.

The researchers found that only about 14 percent of people with lifetime marijuana use disorder receive treatment.