Background: Even occasional use of cannabis may increase the risk of serious mental disease (e.g. schizophrenia). Little has been known about the use of cannabis in Norway; especially among adults.
Material and methods: A representative sample of young men and women were followed up from they were in their teens in 1992 until they were young adults in 2005. During this 13-year period they were asked four times (through a questionnaire) about use of cannabis, their education, job status, income, marital status, parenthood and parental education and social class.
Results: In the mid teens (15 - 16 years), less than 10 % had used cannabis. However, a rather high proportion had their debut in their late teens, as well as throughout their twenties. At the end of the twenties, 40 % of the men and 29 % of the women had used cannabis at some point, and 18 % of the men and 8 % of the women had used cannabis during the previous 12 months. Among the users, 70 % had used the substance 1 - 10 times the last 12 months, while 30 % had a more frequent pattern of use. During the teenage years, there were no associations with parental social class. However, during the twenties, the recruitment base of cannabis use increasingly became socially marginal men who lived aloe and had little education.
Interpretation: Use of cannabis is currently rather prevalent in groups of young adults in Norway, in particular among men. The future incidence of psychosis and schizophrenia may be affected by this.