Cannabis, derived from the plant Cannabis sativa, is the most widely used illicit drug in Australia. Approximately one-third of the population have reported cannabis use at some time in their life, with around 9% reporting use in the past 12 months. Over the past few decades, the proportion of young people who have used cannabis has steadily increased while the age of first use has declined. An earlier onset of use increases the risk for subsequent dependence, while regular use during adolescence predicts later use of other illicit drugs, underperformance in school and mental health problems.