One in 25 adults across the world uses cannabis, despite the risks the illegal drug can pose to their health, experts believe.
Using cannabis regularly can increase the chances of suffering from anxiety, panic attacks and psychotic symptoms as well as lung and heart problems, they warn.
Studies have also suggested that the drug can also increase the risk of having a car crash, although not as much as drinking alcohol.
Researchers said that use of cannabis typically begins when young people are teenagers.
It then goes on to peak when they are in their early to middle 20s, before declining as young people get full-time jobs, marry, and have children.
Cannabis use is thought to be highest in America, Australia and New Zealand, followed by Europe.
However, the researchers believe that use of the drug has been declining across Western Europe in recent years, including in Britain.
Studies suggest the risk of schizophrenia more than doubles in those who have tried cannabis by age 18.
The study, by researchers from the School of Population Health at the University of Queensland, and the National Drug and Alcohol Research Centre at the University of New South Wales, was published in the Lancet medical journal.
By Kate Devlin
October 16, 2009