Does motivation to change mediate the effect of DSM-IV substance use disorders on treatment utilization and substance use?

Evidence suggests that motivation to change may mediate the effect of diagnostic severity on treatment outcome, however, this relationship has not been directly tested. This prospective study tested the mediating effect of motivation to change on the relationship between the severity of DSM-IV substance use disorders at treatment entry and subsequent treatment utilization and substance use. Participants consisted of 150 (89 men and 62 women) alcohol, cocaine, and heroin users entering treatment who completed interviews assessing DSM-IV diagnostic severity (Substance Dependence Severity Scale, SDSS) and substance-specific motivation to change (University of Rhode Island Change Assessment Scale, URICA). All participants were reinterviewed over a 6-month period. DSM-IV alcohol dependence severity predicted less alcohol use and formal treatment use and greater motivation to change and self-help use. Similar associations were demonstrated among cocaine users. Motivation to change alcohol use was not associated with substance use or treatment utilization. The results suggest that alcohol dependence severity has a direct positive effect on motivation to change at treatment entry. However, the effect of alcohol and cocaine dependence severity on treatment utilization and substance use is not mediated by motivation to change substance use at the beginning of a treatment episode.