Figure 1 shows the associations between age of onset of cannabis use (measured as an ordinal variable) and measures of cannabis abuse/dependence, lifetime use of selected illicit drugs (cocaine, stimulants, hallucinogens), and abuse or dependence on these drug categories. This figure shows consistent — and approximately linear — associations between the age of onset of cannabis use and risks of these outcomes: individuals reporting onset of cannabis use before age 16 had rates of these outcomes that were substantially higher than rates among those initiating cannabis use after age 20. Rates of these outcomes were lowest among those reporting no lifetime use of cannabis.
