Risk factors

Risk factors for dual- and poly-use differed from the risk factors associated with sole-use, both in number and type. Mental health predictors such as self-rated depression, emotional problems and learning disabilities tended to be associated with dual- and poly-use, rather than sole-use behaviors, supporting evidence that stress, learning disabilities, emotional regulation problems, and mental health problems (including conduct disorder, depression, and anxiety) are important correlates of adolescent substance use.15,27 These mental health predictors may also be a reflection of the environments that adolescents grew up in. Household tobacco and marijuana use were significantly associated with sole-, dual-, and poly-use, reflecting evidence on the importance of family influences and the home environment on adolescent behaviors.28,29 This finding relates to social cognitive theory and ecological systems theory, as parents, guardians, and older siblings, within an interpersonal home environment, shape the cognitive and behavioural basis of risk behaviors.14 Family or parental cigarette smoking influences adolescent smoking and nicotine dependence.30 Our findings highlight the potential value of family-level treatment approaches to address adolescent substance use.31 We found that adolescents who engage in dual- or poly-use substances had differing risk profiles than those who solely-use substances, and even adolescents who sole-use e-cigarettes or cannabis have differing characteristics, suggesting that certain adolescents may be more protected than others from environmental influences. For example, lower academic grades were associated with a higher likelihood of with dual- and poly-use, but not sole use, consistent with prior research on risk factors for multiple substance use among adolescents.6,32 Studies have found that adolescents that who abstain from tobacco or cannabis substance use are more likely to experience better academic outcomes than adolescents who do use these substances. Academic grades may be a reflection of not just individual student achievement, but also an adolescent’s childhood and surroundings, influenced by factors such as parental socioeconomic status, including parental academic attainment and learning supports.34 Adolescents’ perceived availability of substances influences their decisions and access to substances, with household member use, peer influences, and policy contributing to these perceptions.27,35,36 As cannabis is becoming more readily available, especially in states like Massachusetts where a recreational adult cannabis market has been legalized,37 perceived availability and acceptability of cannabis at a population level may encourage increased adolescent use of such legalized substances.38 Research has found that adolescents report higher intention to use cannabis if it is legal.36 The legalization of recreational adult cannabis may disproportionately impact adolescents who use cannabis, both solely and with other substances, relative to adolescents who do not use cannabis. Therefore, policymakers and public health practitioners should consider the impact of changing substance use policies and opening distribution of more cannabis dispensaries, as this may widen health disparities in use among adolescents who engage in dual- and poly-use, especially those who are struggling academically in school or experience mental health problems.