Although the co-occurrence of substance use behaviors and depression is well-established, little research has investigated age trends in these associations. Rates of substance use and depression both show notable age trends and both peak in adolescence. It is plausible that the associations between substance use behaviors and depression are also stronger during adolescence, as the profound physiological and social developmental processes occurring during adolescence may heighten vulnerability. Substance use in early adolescence is less normative and typically occurs among youth who face a myriad of risk factors, including adverse early life events, lack of parental involvement, or family and peer substance use (Green et al., 2012); substance use becomes more normative with age (SAMHSA, 2014). Thus, age-varying associations between substance use and depression may reflect age-varying risk profiles of substance users due to changes in the meaning and context of substance use over time. Alternatively, stronger associations in adolescence may reflect the imbalance in arousal and regulation that characterizes the developing adolescent brain: pubertal maturation increases emotional arousal, sensation-seeking, and reward orientation, yet adolescents do not have fully formed executive
