Abstract Comorbidity of substance abuse disorders (SUD) and psychiatric disorders is one of the most important areas of investigation in contemporary drug abuse treatment research. This study examined the impact of psychiatric comorbidity on the treatment of 182 adolescent drug abusers in a randomized clinical trial comparing family and individual cognitive-behavioral therapy. Three distinct groups of adolescent substance abusers were compared: (1) Exclusive Substance Abusers (SUD only); (2) Externalizers (SUD + externalizing disorder); and (3) Mixed Substance Abusers (SUD + externalizing and internalizing disorder). The purpose of this study was to determine whether adolescents in these comorbid groups differed in clinical presentation and treatment response. More severe comorbidity was associated with greater family dysfunction and being female and younger at intake. An examination of substance use trajectories over time indicated that the Mixed group initially responded to treatment but returned to intake levels of substance use by 1 year post-discharge.
