Many proponents of cannabis feel that their drug of choice is better than tobacco or alcohol. They say that it is not addictive, that it is natural, that no one has ever died of an overdose from smoking marijuana. But new research indicates that it may not be so black and white: researchers in Australia have found that people who frequently smoke marijuana as teens are more likely to develop anxiety disorders during adulthood.

Lead investigator Louisa Degenhart, from the National Drug and Alcohol Research Centre at the University of New South Wales, and her colleagues conducted a longitudinal study over the course of 15 years, focusing on anxiety disorders and depression. Over the course of a decade and a half, 1,943 young adults were recruited from an area high school, the researchers observed the teens from 14 years old to 29 years old.

While researchers found no correlation between cannabis use and depression, they found that, for teenagers who smoked weed at least once a week, their risk of developing an anxiety disorder was double that of their peers. For teenagers who continued smoking into adulthood, their risk of anxiety disorders were triple that of their non-smoking peers.

Anxiety is a huge problem in Australia, as it is the leading psychological problem there, affecting 14 percent of adults during any given 12-month period. Despite the increasing societal acceptance of and attention to depression, anxiety is also the number-1 mental health disorder in the United States. Anxiety disorders affect a total of 40 million adults, or 18 percent of the adult population, a year.

Investigators have been unable to ascertain the reason for the correlation, and have not even distinguished whether the relationship is causal or simply correlational. Degenhart, who has been studying the link between cannabis and psychiatric disorders for at least a decade, suggests that the introduction of pot to a developing brain could cause an anxiety disorder to develop. However, the researchers have not ruled out the possibility that some of the people who are predisposed to smoking weed are the same people who are predisposed to developing anxiety disorders.

Degenhart also said that, in animal models, the effects of cannabis are seen well after the animals stop the intake of marijuana.

The study was published in the journal Addiction.