Marijuana use appears to have decreased among most European and North American adolescents between 2002 and 2006, and those who went out with friends on fewer evenings of the week were less likely to report using the drug, according to a report in the February issue of Archives of Pediatrics & Adolescent Medicine, one of the JAMA/Archives journals.

"Cannabis [marijuana] use among young people is a serious public health concern," the authors write as background information in the article. Recent evidence links marijuana use to motor vehicle accidents, injuries, inflammatory and cancerous changes in the airways and mental health problems, including depression. Long-term detrimental effects include poor academic performance and failure to complete schooling, impeding development and hampering future career opportunities.

"One factor that may help explain why adolescents engage in cannabis use is association with cannabis-using peers, which can increase the availability of cannabis and socially influence use," the authors write. To investigate this link and also trends in marijuana use over time, Emmanuel Kuntsche, Ph.D., of the Swiss Institute for the Prevention of Alcohol and Drugs Problems, Lausanne, and colleagues analyzed data from 93,297 15-year-old students who participated in the Health Behavior in School-Aged Children study. Participants in 31 countries (mostly in Europe and North America) were surveyed in 2002 and again in 2006 about marijuana use and the number of evenings per week they usually spend out with their friends, among other topics.

During the four-year study period, marijuana use decreased in most of the countries, with the most significant declines in England, Portugal, Switzerland, Slovenia and Canada. Increases were observed in Estonia, Lithuania, and Malta and among Russian girls. The number of evenings out with friends also declined in most countries during the same time period, although there was a wide range in averages, from about one evening per week for Portuguese girls to more than three evenings per week among boys and girls in the Ukraine, Russia, Scotland, Estonia and Spain.

"The more frequently adolescents reported going out with their friends in the evenings, the more likely they were to report using cannabis," the authors write. "This link was consistent for boys and girls and across survey years. Across countries, changes in the mean [average] frequency of evenings spent out were strongly linked to changes in cannabis use."

Besides a decline in evenings out with friends, potential reasons for the decline in marijuana use include prevention efforts, availability or changes in teen preferences. It is more difficult to pinpoint factors behind the decline in evenings out, the authors note. New forms of communication, such as e-mail and text messaging, may have replaced some face-to-face interactions, or that the high rate of marijuana use in 2002 may have increased parental concerns about substance use and made access to the drug and evenings out more difficult.

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"This overview of trends in 31 countries and regions provides policy makers with important information on the prevalence and amount of change in cannabis use among boys and girls in their countries," the authors write. "There is a great need to learn more about the nature of evenings out with friends and related factors that might explain changes in adolescent cannabis use over time. Because there are many benefits to adolescent social interaction, it is important to determine how best to foster it without unduly increasing exposure opportunities for cannabis use."

This study was supported by the Swiss Institute for the Prevention of Alcohol and Drug Problems and a grant from the Swiss Federal Office of Public Health.

Editorial: Reducing Social Time for Teens Not an Ideal Prevention Method

"What we have gained from this well-designed international study is further convincing evidence that unsupervised social time is a critical ingredient for cannabis use for many young people," write John E. Schulenberg, Ph.D., and Patrick M. O'Malley, Ph.D., of the University of Michigan, Ann Arbor, in an accompanying editorial.

"This might lead some to suggest a simple intervention of reducing unsupervised time with friends by, for example, increasing structured time with friends, increasing school and work time or increasing alone time," the authors write. "However, this strategy may have unintended consequences for many adolescents. An important part of adolescence is exploring and forming friendships, having bonding experiences and finding a safe haven with friends away from adult supervision."

"Thus, rather than trying to reduce socializing with friends, a more complicated but possibly more successful approach to intervention would help young people find activities together that do not promote marijuana use," they conclude.

Preparation of this article was supported in part by a grant from the National Institute of Drug Abuse.