Does psychiatric comorbidity affect drug abuse treatment outcome? A prospective assessment of drug abuse, treatment tenure and infectious diseases in an Israeli methadone maintenance clinic

Objective: The influence of psychiatric comorbidity in drug addicts on therapeutic outcome is an important unresolved issue. We studied the links between patterns of psychiatric comorbidity and psychological distress with treatment outcome variables. Method: 151 methadone maintenance patients underwent a structured clinical interview, twice-weekly urinalysis for traces of drugs of abuse, and completed psychological distress and risk-taking questionnaires for periods of up to three years. Treatment tenure, demographics and hepatitis C status were recorded. Results: High levels of lifetime (82.8%) and current (66.2%) Axis I psychiatric comorbidity were mostly anxiety and affective disorders many of which were substance induced. Patients with current psychiatric comorbidity had significantly more current substance use disorders, although they did not abuse more drugs or remain in treatment less time than patients with no current psychiatric comorbidity. Patients with a lifetime Axis 1 disorder remained in treatment longer. Severity of psychological distress was related to current substance-related diagnoses, benzodiazepine abuse, higher methadone dosage, risk-taking behavior and the presence of hepatitis C. Conclusions: Severity of psychological distress, but not comorbid psychiatric disorders, has a major negative association with treatment outcome of patients receiving methadone maintenance treatment (MMT). Surprisingly patients with comorbid mental illness seem to remain in treatment longer than those without. Therapeutic efforts should also focus on treating subjective distress and its possible influence upon drug use behavior.