Twelve Month Mental Health, Substance Use and Service Use Trajectories Among Emerging Adults in Outpatient Substance Use Disorder Treatments

Objectives: The prevalence of mental health problems among emerging adults (EAs) remains high, and EAs frequently do not engage in empirically supported treatments to ameliorate these conditions (Blanco et al., 2008; Chan et al., 2008).  Little is known about how emerging adults respond to treatment and what pattern of services they receive contingent upon their presenting substance use and mental health severity.  Thus, the purpose of this study was to examine service utilization, substance use, and mental health trajectories among emerging adults initially presenting to substance use disorder treatment agencies.       

Method.Emerging adults participating in longitudinal studies of substance use disorder treatment outcomes who completed all follow up waves and had no missing data on clustering variables (i.e., 3, 6, and 12 months) were selected for analysis (n=579, mean age =19.8, 30% female).  Although effect sizes were small, analyses revealed that the analysis sample had higher substance use frequency and mental health severity.   Cluster analyses were conducted using squared Euclidean distance on four variables including substance use frequency, emotional problems, substance abuse treatment utilization, and mental health treatment utilization. Trajectory cluster solutions were analyzed based on multiple criteria, including: cluster eigenvalues, cluster size, the percent of variance explained for each cluster measure, the percent of variance explained in the joint distribution (1-Wilks Lambda), and parsimony/interpretability.  Trajectory clusters with four and five subgroups met most criteria, and the simpler four group solution was selected.  In ANOVA analyses we compared each trajectory cluster on baseline characteristics.

Results.  Four trajectories were identified, including: low severity improvement (i.e., low severity clients improving with low service utilization (56.8%)) , moderate persistent problems (i.e., persistent substance use and mental health problems with low service utilization (29%)), primary mental health treatment (i.e., high mental health treatment utilization with moderate mental health problems and low substance use (6.2%)), and  primary substance use disorder treatment (i.e., high and increasing substance use disorder treatment with decreasing substance use and lower mental health problems (7.9%).  These trajectory groups differed on a number of baseline characteristics.  For example, a significantly higher percent of emerging adults in the moderate persistent problems (67%) and primary substance use treatment groups (76%) met criteria for past year dependence when compared to the low severity improvement group (45%).  

Conclusion: Four distinct trajectories emerged, which differed on substance use severity, mental health severity, and both mental health and substance use treatment utilization over the course of 12 months.   Findings are discussed in the context of designing and monitoring treatment outcome study findings and coordinating care between service sectors.