The Longitudinal Impact of Intrinsic Motivation on Substance Use Severity in Schizophrenia and its Patterns in Men and Women

Schizophrenia is a complex and disabling psychiatric disorder that results in significant burden and challenges to those who suffer from it, their families, and to our larger society. One of the most vexing problems facing individuals with schizophrenia today is the co-occurrence of substance use disorders (SUDs). Longitudinal evidence indicates that many individuals with schizophrenia and comorbid SUD exhibit severe patterns of substance use over the course of the disorder, such that few achieve sustained remission or recovery. Intrinsic motivation deficits are promising potential contributors to substance use severity in this population, and consequently might serve as effective treatment targets. There is also evidence to suggest that women show less deficit in intrinsic motivation than men. To date, measurement in this area has been limited, and no study has investigated the longitudinal relations between prospective changes in intrinsic motivation and changes in substance use severity among individuals with schizophrenia and comorbid SUD. This study makes use of baseline, 6-, and 12-month follow-up data from patients with schizophrenia and comorbid SUD (n = 535 at baseline; n = 219 at 6-months; n = 150 at 1-year) selected from the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) study to: (1) extend validation of a promising new measure of intrinsic motivation developed by Nakagami, Xie, Hoe, and Brekke (2008) for schizophrenia to schizophrenia and comorbid SUD; (2) elucidate its longitudinal relations with substance use severity among this population; (3) and examine whether such relations vary across genders. A comprehensive psychometric analysis was used to examine the factor structure, reliability, and retest reliability of the instrument in this population; and hierarchical linear regression and hierarchical linear modeling were among the analytic methods used to examine the cross-sectional and longitudinal relations between intrinsic motivation and substance use severity. Psychometric results supported the reliability and retest reliability of the intrinsic motivation measure when applied to schizophrenia and comorbid SUD, but also revealed a potential shift in the latent factor structure of the instrument. Cross-sectional findings revealed a significant negative prediction of intrinsic motivation by alcohol and drug use severity after adjusting for demographic and clinical confounds, neurocognition and negative symptoms. Longitudinal results with intrinsic motivation strengthened the findings garnered in the cross-sectional analyses. Evidence was found suggesting longitudinal intrinsic motivation change is a salient incremental predictor of reductions in patient’s alcohol/ drug use severity, above and beyond the effects of age, illness chronicity, overall psychopathology, comorbidity status, and phase 1 randomization medication effects. Analyses of relations with gender indicated little to no cross-sectional associations between intrinsic motivation and substance use severity, and gender did not moderate the longitudinal association between intrinsic motivation and substance use severity. These findings suggest that changes in intrinsic motivation may be uniquely associated with changes in substance use severity in schizophrenia and comorbid SUD. Future research will need to replicate these findings, while focusing on intervention efforts that seek to target the intrinsic motivation deficits of schizophrenia and comorbid SUD, to help offset the severe and destabilizing effects exacted by substance use severity in this population.