Malmö Treatment Referral and Intervention Study (MATRIS)-36-month follow-up on retention and substance use among patients referred from needle exchange to opioid agonist treatment-The role of stimulant use at baseline.

Introduction: Opioid use disorder (OUD) is the leading cause of overdose morbidity and mortality globally. Retention in opioid agonist treatment (OAT) is crucial as it effectively reduces overdose mortality among individuals suffering from OUD. Previous research on treatment retention among heroin-dependent individuals referred from needle exchange programs (NEP) to OAT is scarce, and with predictors for retention in OAT being somewhat inconclusive, further investigations into this subject is of great interest. The aim of our study was to assess 36-month treatment outcomes-defined as retention and illicit drug abstinence-and predictors of OAT discontinuation.

Methods: This is a longitudinal cohort study of 71 study subjects successfully referred from a NEP to OAT. Participants were included between October 2011 and April 2013 and followed for 36 months. The study collected data from a structured baseline interview and from patient records, including laboratory data.

Results: At the 36-month follow-up, retention was 51 % (n = 36), with mean days in treatment of 422 for those who discontinued treatment. Amphetamine use during the 30 days before inclusion was positively correlated with treatment discontinuation (AOR 1.22 [95 % CI 1.02-1.46]). No statistically significant association with retention was seen for gender, age, suicide attempt prior to treatment, or benzodiazepine use during 30 days prior to treatment. Opiate use and use of other substances were reduced over time, with major reductions occurring during the first 6 months.

Conclusions: Hitherto, baseline factors predicting retention in OAT have been insufficiently demonstrated. Active referral from NEP to OAT is effective when it comes to long-term retention and reduction of substance use while in treatment. Except from use of amphetamine, the use of other substances prior to OAT was not associated with treatment discontinuation. Further and in-depth analyses of baseline predictors are of importance for OAT retention.