As more and more people in the US are sparking up, so are debates about marijuana legalization. A total of 23 states now have medical marijuana laws, while four states have legalized recreational use of the drug. Now, a new study investigates to what extent marijuana use has increased among the general population, reflecting how attitudes have changed.

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In the US, medical marijuana laws are in effect in 23 states, and the new study reveals that marijuana use doubled from 2001-2013.

The study – led by Bridget F. Grant, PhD, of the National Institute on Alcohol Abuse and Alcoholism – is published in JAMA Psychiatry.

Although laws and attitudes regarding marijuana use are changing in the US, the researchers note that little is known about how marijuana and associated use disorders have changed in the 21st century.

They note that fewer Americans are viewing marijuana use as risky, despite studies showing that use or early use of the substance is linked to increased risk for certain outcomes, including cognitive decline, psychosocial impairments, car crashes, hospital visits, poor quality of life, other drug use and cannabis-withdrawal syndrome.

To further investigate past-year prevalence rates of marijuana use, Grant and her team used face-to-face interviews conducted in surveys of two nationally representative samples of adults in the US.

Results showed that past-year marijuana use prevalence increased from 4.1% in 2001-2002 to 9.5% in 2012-2013.

The researchers say there were notable increases among women, black and Hispanic populations, those living in the South and people who are middle-aged or older.

Additionally, the investigation revealed that prevalence of marijuana use disorder – which includes abuse or dependence – also increased during this time period; it went from 1.5% in 2001-2002 to 2.9% in 2012-2013.

The researchers say this means that nearly 3 in 10 users of marijuana in the US had a diagnosis of a marijuana use disorder, which equates to around 6.8 million Americans.

Interestingly, however, among already-existing marijuana users, the prevalence of marijuana use disorder actually decreased to 30.6% in 2012-2013 from 35.6% in 2001-2013. The authors do not speculate on potential reasons for this decrease, but changing attitudes toward marijuana use – and users – could be at play.

“In summary, while many in the US think prohibition of recreational marijuana should be ended, this study and others suggest caution and the need for public education about the potential harms in marijuana use, including the risk for addiction,” write the authors.

They continue:

”As is the case with alcohol, many individuals can use marijuana without becoming addicted. However, the clear risk for marijuana use disorders among users (approximately 30%) suggests that as the number of US users grows, so will the numbers of those experiencing problems related to such use.”

They add that, in light of changing attitudes and laws regarding marijuana, “a balanced presentation of the likelihood of adverse consequences of marijuana use to policy makers, professionals and the public is needed.”

Medical News Today recently reported on a study that suggested, for the first time, college students are smoking more marijuana than cigarettes daily, with around 1 in 17 students smoking the substance every day.