In conclusion, the results obtained in this study demonstrate that magnitude of transmissible risk measured on a continuous scale covaries negatively with age at the time of first alcohol and cannabis use presaging AUD and CUD. The observation that age at the time of first substance use also fully mediates the association of transmissible risk and development of both disorders indicates that onset age is an indicator of magnitude of the individual’s vulnerability predisposing to SUD. These findings underscore the importance of directing prevention at high-risk youths prior to first substance exposure.
