Using marijuana may lead in short order to using even more marijuana as well as abusing other drugs and alcohol, suggests a new analysis of US data. Based on national surveys three years apart, researchers found that adults who reported using pot in the first survey were two to nine times more likely to have a substance abuse problem by the time of the second survey. These risks should be considered not only by patients and doctors, but also by policymakers in states where marijuana may be up for legalization for recreational or medical use, experts say. "Patients who may be considering using cannabis should know that by using cannabis they are approximately doubling their risk of developing a drug use disorder over the next few years," said senior study author Dr. Mark Olfson of Columbia University Medical Center and the New York State Psychiatric Institute in New York City. "Patients who already use cannabis should be aware that increasing their use may further increase their risk of developing a substance use disorder, while reducing or stopping their cannabis use is likely to reduce that risk," he told Reuters Health by email. Olfson and colleagues analyzed survey responses from a nationally representative sample of US adults interviewed in 2001-2002 and again in 2004-2005. More than 34,650 people responded, almost evenly split among men and women, with a mean age of about 45. In the first survey, 1,279 individuals reported using cannabis. Three years later, that was linked to a nearly three times higher rate of abusing alcohol compared to people who didn't use cannabis in the first survey. The risk of abusing other drugs or being dependent on tobacco was twice as high, and the risk of having a cannabis abuse disorder by the second survey was nine times higher.