Personality characteristics of substance abusers: an MCMI cluster typology of recreational drug users treated in a therapeutic community and its relationship to length of stay and outcome.

The purpose of this investigation was to define homogeneous personality subtypes among substance abusers treated in a long-term, inpatient, drug-free therapeutic community and to determine how the resulting typology was related to length of stay and treatment outcome. A hierarchical agglomerative cluster analysis was performed on the Millon Clinical Multiaxial Inventory (MCMI) scale scores of 235 admissions to a therapeutic community. Five cluster types emerged, which were similar to typologies found in studies with alcoholic inpatients. A concordant solution evolved when a different clustering algorithm was used with the same sample and when clustering was done with a different group of substance abusers. As hypothesized, clusters of patients with average MCMI elevations that indicated avoidant, schizoid, and antisocial qualities tended to stay in treatment fewer days and relapsed earlier during the 1-year follow-up. The implications for substance abuse treatment are discussed.