Co-morbid psychiatric symptoms and clinical outcomes for treatment – seeking opioiddependent patients prescribed methadone opioid substitution therapy (OST): a 7 year prospective cohort study

Mental illness and opioid dependence are common comorbidities that may affect individuals’ clinical outcomes on Opioid Substitution Therapy (OST) treatment. Though many associations have been described, the long-term impacts of common comorbid mental illnesses on OST treatment progress remain poorly understood. This is particularly relevant when there is a renewed drive to improve progress towards recovery in OST patients.

Aims: Using the scaled General Health Questionnaire (GHQ28) and other validated instruments, this prospective cohort study aimed to describe the prevalence of psychiatric caseness in a large representative cohort of methadone-prescribed substance misusers and to explore the relationships between these psychiatric comorbidities, clinical process and long-term outcomes over 7 years.

Design and Methods: A baseline cohort of 623 methadone OST patients was assessed using a range of validated instruments. Seven year follow up data were collected using casenote review and health informatics procedures.

Results: GHQ-derived psychiatric caseness was identified in 58.4% at baseline but showed no significant associations with clinical process or 7-year outcomes. Post-Traumatic Stress Disorder was more prevalent than previously described while ADHD was less prevalent. Significant associations were demonstrated between baseline psychiatric comorbidities and substance misuse risk behaviours, clinical processes and associated 7-year outcomes.

Conclusions and discussion: Psychiatric comorbidity is common though studies show considerable variation in prevalence. Common psychiatric comorbidities impact upon long term substance use outcomes in OST patients. The relationships, however, are complex. These relationships must be better understood to improve OST outcomes and opportunities for progress towards recovery.