Elkins, I.J., Saunders, G.R.B., Malone, S.M., Wilson, S., McGue, M., & Iacono, W.G. (2018) Mediating pathways from childhood ADHD to adolescent tobacco and marijuana problems: Roles of peer impairment, internalizing, adolescent ADHD symptoms, and gender. Journal of Child Psychology and Psychiatry, 59(10), 1083-1093. PMCID: PMC6169803

Elkins, I.J., King, S.M., McGue, M. & Iacono, W.G. (2006) Personality Traits and the Development of Nicotine, Alcohol, and Illicit Drug Disorders: Prospective Links from Adolescence to Young Adulthood. Journal of Abnormal Psychology, 115, 26-39.

The personality traits constraint (CN) and negative emotionality (NE) have been more (CN) or less (NE) consistently associated with alcoholism. The authors examined the association of personality at age 17 with timing of onset and with prospective prediction of nicotine, alcohol, and illicit drug disorders 3 years later in a twin sample (569 females; 432 males). Earlier onset of alcohol and drug disorders (by age 17) was related to significantly lower CN compared with later onsets (by age 20); high NE was related to either onset. NE, as well as CN, uniquely predicted new onsets of all 3 types of substance use disorders by follow-up, with preexisting substance disorders taken into account. Personality traits confer generalized risk for developing any substance disorder, though some traits are more strongly linked with some substance disorders than with others.

King, S.M., Iacono, W.G. & McGue, M. (2004). Childhood Externalizing and Internalizing Psychopathology in Prediction of Early Substance Use. Addiction, 99, 1548-1559.

Aims: To examine the prospective relationships between childhood externalizing and internalizing disorders and substance use in early adolescence.
Design: Longitudinal, community-based study of twins (aged 11 at intake; aged 14 at follow-up).
Setting and participants: The sample was composed of twins participating in the Minnesota Twin Family Study, an epidemiological sample of twins and their families representative of the state population of Minnesota. A total of 699 twin girls and 665 twin boys participated at both time-points.
Measurements: Twins participated in in-person, life-time diagnostic assessments of the following childhood DSM III-R externalizing and internalizing disorders at age 11: conduct disorder, oppositional defiant disorder, attention deficit hyperactivity disorder, major depressive disorder and in addition, for girls only, overanxious disorder and separation anxiety disorder. At ages 11 and 14, substance use and abuse were assessed.
Findings: Externalizing psychopathology predicted having tried alcohol, nicotine and cannabis by age 14 as well as regular and advanced experience with these substances. Internalizing disorders showed weak effects, with only major depression at age 11 showing a significant relationship with substance use at age 14.
Conclusion: The results suggest that externalizing psychopathology is a robust prospective predictor of a variety of early onset substance use behaviors and is systematically related to degree of substance use involvement. The results also suggest that depression may predict initiation of licit substance use in early adolescence.

Taylor, J.T., Malone, S., Iacono, W.G., & McGue, M. (2002). Development of substance dependence in two delinquency subgroups and non-delinquents from a male twin sample. Journal of the American Academy of Child and Adolescent Psychiatry, 41, 386-93.

Objective: The effect of delinquency subtype on the development of substance dependence symptoms was examined. It was proposed that early-onset delinquents possess characteristics that increase their likelihood of developing substance dependence problems earlier and more rapidly than late-onset delinquents and nondelinquents.
Method: The development of alcohol, nicotine, and cannabis dependence symptoms (DSM-III-R) was examined over a 6-year period of adolescence (age 11–17) among 36 early-onset delinquent, 86 late-onset delinquent, and 25 nondelinquent boys from a large epidemiological twin sample. Multilevel/random coefficients models were used to compare groups on the rate of growth in number of symptoms over time.
Results: As expected, early-onset delinquents showed an earlier onset and a faster rate of increase in the number of cannabis and nicotine dependence symptoms than late-onset delinquents and controls. Both delinquent groups had a more rapid increase in alcohol dependence symptoms than controls.
Conclusions:
The data showed that early-onset delinquency is associated with earlier onset of substance use disorder symptoms and more rapid acceleration of problems with drugs than late-onset delinquency. Treatments for boys with early-onset delinquency should account for their increased risk for drug use problems in adolescence and the potential effects of those problems on the course of antisocial behavior.
J. Am. Acad. Child Adolesc. Psychiatry, 2002, 41(4):000–000.