Childhood psychopathology can cause an array of adverse outcomes later in later life, including substance use disorders (SUDs). Perhaps because substance abuse is thought to be on the externalizing continuum, the prospective association between childhood externalizing disorders and SUDs is more frequently studied than the association with internalizing disorder. Indeed, research on attention-deficit/hyperactivity disorder (ADHD), oppositional defiant disorder, and conduct disorder (CD) quite consistently demonstrate that these disorders are associated with increased SUDs risk in later life.1 However, although it is often thought that only externalizing disorders in childhood increase the risk of SUDs in later life, there is evidence, albeit more fragmented, for a similar association between internalizing disorders in childhood and later substance use.1 Because internalizing and externalizing disorders are often comorbid, it is vital to investigate their joint effect on the developmental trajectory toward SUDs. So far, this trajectory has mainly been studied from an externalizing perspective, but Virtanen et al.2 studied this prospective association with internalizing disorders as the start point, while considering the possibility of biological sex-specific patterns.
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