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Conjoint Developmental Trajectories of Young Adult Substance Use
Portions of this paper were presented at the 112th Annual Convention of the American Psychological Association in Honolulu, HI. Preparation of the work was supported by National Institute on Alcohol Abuse and Alcoholism Grants AA12383 and AA13938 to Kristina M. Jackson. The Monitoring the Future project, from which the data were obtained, is funded by the National Institute on Drug Abuse Grant DA01411 to Lloyd D. Johnston. The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the NIH.
Reprint requests: Kristina M. Jackson, PhD, Research Assistant Professor, Brown University, Center for Alcohol and Addiction Studies, Box G-S121-4, Providence, RI 02912; Fax: (401) 863-6647; E-mail: kristina_jackson@brown.edu
Abstract
Background. Despite the prominence of comorbidity among substances and the recent attention focused on trajectory-based approaches to characterizing developmental change, little research in the substance use field has simultaneously considered both course and comorbidity.
Methods. Using nationally representative panel data from the Monitoring the Future Project (MTF; n = 32,087; 56% female; 82% Caucasian), we identified developmental courses of heavy drinking, smoking, and marijuana use using 4 waves of data spanning ages 18 to 26 in a multi-cohort young adult sample. Comorbidity was examined by cross-classifying group membership in substance use trajectories. Finally, the extent to which risk factors (sex, race, alcohol expectancies, delinquency, sensation seeking, depressive affect, religiosity, academic achievement, and parent education) accounted for combinations of comorbidity that occurred at a rate greater than chance was examined.
Results. For each substance, we identified 4 courses of substance use that were largely consistent with those found in the literature (chronic high use, late-onset use, developmentally limited use, and low-use), with a fifth moderate smoking group. Heavy drinking, smoking, and marijuana use were each highly associated, and distinct patterns of comorbidity were evident, with greatest agreement along the diagonal. All risk factors explained comorbidity to some degree, with delinquency, sensation seeking, alcohol expectancies, and religion in particular predicting combinations of comorbidity that were characterized by early onset and chronic high use.
Conclusions. Cross-substance trajectory concordance was high, with parallel changes in substance use over emerging adulthood. This suggests similar developmental timing of use, perhaps due to the experience of developmental transitions that have a common influence on use of different substances. Prediction of combinations of comorbidity characterized by early onset and persistently high use suggests that to some extent, individuals use multiple substances because of a common vulnerability to each, rather than directional relations among substances (e.g., cross-tolerance, cueing).