Long-term cannabis use can have detrimental effects on the adolescents such as 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.

During the study, Emmanuel Kuntsche, PhD, of the Swiss Institute for the Prevention of Alcohol and Drugs Problems, Lausanne, analyzed data from 93,297 15-year-old students who participated in the Health Behaviour 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.

"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," they added.

The authors said that 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.

Since 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.