A study on the perceived risk of regularly using cannabis and the characteristics associated with these perceptions found that non-white, low-income women over the age of 50 were most likely to perceive a risk in using the drug. Least likely were those 12 to 25 years old, with a high school diploma or more, and a total family income above $75,000. The study by researchers at Columbia University's Mailman School of Public Health with colleagues at Johns Hopkins University is the first to describe changes across time in perceived risk of regular cannabis use in the U.S. population 12 years and older. Results are published in the journal Drug and Alcohol Dependence.

Data from 614,579 individuals who took part in the 2002-2012 National Survey on Drug Use showed that past-year daily cannabis use has increased significantly between 2002 and 2012. The results also show that in 2002 participants were significantly more likely to associate risk with regular cannabis use compared to individuals interviewed in the years 2008 through 2012. In 2002, 51 percent of all survey participants believed there was a great risk associated with regular cannabis use versus 40 percent of participants in 2012. Findings were adjusted for sex, age, race/ethnicity, education, total family income, past year cannabis use status, and survey year. Regular use of marijuana was defined as once or twice a week.

"The changing perception about marijuana risk may at least partially be explained by the increasing number of states that legalized medical marijuana during 2008 and after," said Silvia Martins, MD, PhD, associate professor of Epidemiology at the Mailman School of Public Health.

Females were nearly two times more likely to perceive risk in regular marijuana use compared with males, yet the perceived risk among women decreased from 59 percent in 2002 to 47 percent in 2012. The number of female users remained stable in 2012 compared to 2002, however the number of female regular users slightly increased in the same time period.

Non-daily cannabis use in the past year varied between 2002 and 2012, but did not change dramatically when comparing the years 2002 and 2012 directly (9.7 percent vs. 10.2 percent, respectively).

Users in the past year were less likely to perceive a risk from regular cannabis use. Daily users were 96 percent less likely than non-users, and non-daily users were 89 percent less likely than past year non-users to have this perception.

"The sex differences in perceived risk of regular cannabis use observed in our study are consistent with reports from others showing male-female differences in perceived risk of substance use in general," said Silvia Martins, MD, PhD, associate professor of Epidemiology at the Mailman School of Public Health. "In addition, interestingly, individuals with a high school education or greater were significantly less likely to perceive great risk of regular cannabis use than those with less than a high school education, findings partially corroborated by results from Gallup polls indicating that adults with a college education compared to those without are more likely to support legalization of cannabis."

Regular cannabis use has been associated with financial difficulties, low energy levels, dissatisfaction with productivity levels, sleep and memory issues, and relationship and family problems. Most individuals receiving treatment for cannabis use disorder -- defined as clinically significant impairment -- report difficulty quitting, and experience a withdrawal syndrome after cessation.

"Perceived risk is an important factor in deciding whether or not individuals will engage in health-related behaviors, such as cigarette smoking or binge drinking, for example,," said Dr. Martins. "Continually evolving regulations in the U.S. have the potential to impact perceived risk of cannabis use, which may influence individuals' decisions to first try or use cannabis."

A 2012 Mailman School study led by Dr. Magdalena Cerda showed that adults living in states with medical cannabis laws until 2004 had higher odds of cannabis use than residents of states without such laws. Prior to 2008, 11 states had legalized medical marijuana; today, an additional 12 states and Washington D.C. passed legislation regarding medical marijuana.