typically means longer than average lifetime exposure to substances of abuse and, even more importantly, exposure during a critical period of brain development, with the potential for serious and long-lasting consequences (15, 16). Additionally, risk for abuse or dependence is substantially higher in early initiators of alcohol (17–19), nicotine (20, 21), and cannabis (22, 23). Thus, substance use in childhood or early adolescence is an early warning sign of possible substance-related problems later in life.
