Changes in substance use in patients receiving opioid substitution therapy and resulting clinical challenges: a 17-year treatment case register analysis.

Background: Although the beneficial effects of opioid substitution for the reduction of heroin use are well established, its effect on other substance use is unclear. We aimed to evaluate short-term and long-term changes in substance use in opioid-dependent patients on opioid substitution therapy. We focused on frequent use of heroin, cocaine, benzodiazepines, and alcohol under naturalistic conditions (ie, with non-selected patients and clinical practice as usual) over 17 years.

Methods: This was a treatment case register analysis. Data were obtained from the treatment case register of the canton of Zurich, Switzerland, which included information for 8962 patients (122 399 case report forms) who received substitution therapy with methadone or buprenorphine between 1998 and 2014. The main focus of our study was to evaluate long-term changes in frequent substance use of patients on opioid substitution therapy, together with the associations between individual, treatment, and environmental factors and substance use, including short-term changes at first treatment entry. Data were analysed using a generalised estimating equation that accounted for individual, treatment, and environmental factors. Frequent use was defined as substance use on at least 5 days per week.

Findings: The most frequent use of heroin (odds ratio [OR] 5·30, 95% CI 4·63-6·08; p<0·0001), cocaine (2·30, 1·95-2·71; p<0·0001) and, to a lesser extent, benzodiazepines (1·34, 1·17-1·54; p<0·0001) and alcohol (1·21, 1·08-1·35; p=0·0007), was found in previously untreated individuals compared with patients already receiving treatment 6 months after starting opioid substitution therapy, corroborating a strong effect of initiating substitution therapy. Frequency of substance use was associated with the year of evaluation: frequent use of heroin (OR per decade 0·56, 0·52-0·60; p<0·0001) and cocaine (0·63, 0·58-0·68; p<0·0001) significantly decreased between 1998 and 2014, while frequent alcohol use increased (1·15, 1·08-1·23; p<0·0001). In 2014, frequent alcohol use was observed in 990 (22·5%) of 4400 patients on opioid substitution therapy.

Interpretation: Frequent use of alcohol during opioid substitution therapy significantly increased during the observation period, whereas there was a decline in frequent use of heroin and cocaine. Given the high infection rates with hepatotoxic viruses and the increasing liver-related mortality rates in patients on opioid substitution therapy, these findings suggest that frequent alcohol use increasingly constitutes a therapeutic challenge in opioid substitution therapy.

Funding: None.