Trends in polysubstance use among patients in methadone maintenance treatment in Ireland: Evidence from urine drug testing 2010–2020

Introduction

The benefits of methadone maintenance treatment (MMT) may be compromised by the continued use of other substances during treatment. Polysubstance use has been identified as a major contributing factor to treatment discontinuation, a known risk factor for drug overdose. We examined trends in immunoassay drug positivity rates for amphetamines, benzodiazepines, cannabis, cocaine and opioids, and (2) trends in polysubstance positivity rates for drug combinations associated with increased risk of drug overdose among patients attending the national drug treatment centre in Ireland for MMT between 2010 and 2020.

Methods

Repeated cross-sectional study of patients attending the national drug treatment centre (NDTC) for MMT (total N = 1942) between 2010 and 2020, focused on urine drug samples provided for testing to the NDTC clinical testing laboratory (n = 221,564). Samples were analysed using immunoassay during the study period. Mixed-effects logistic regression models evaluate time trends in drug positivity. A random intercept accounts for repeat testing of individual patients. The study reports Adjusted Odds Ratios (AOR) for time (per year) with 95 % Confidence Intervals (95 % CI).

Results

Drug positivity rates increased over time for benzodiazepines (AOR 1.02, 95 % CI 1.01–1.03, p < .0001), cannabis (AOR 1.06, 95 % CI 1.05–1.08, p < .0001) and cocaine (AOR 1.28, 95 % CI 1.27–1.29, p < .0001), with decreasing trends for opioids (AOR 0.91, 95 % CI 0.91–0.92, p < .0001). Methadone and benzodiazepines were co-detected in over two-thirds of all samples during the study period. Co-detection of methadone and benzodiazepines with cocaine was also found to be increasing (AOR 1.24, 95 % CI 1.23–1.25, p < .0001), with weighted polysubstance positivity rates reaching 29.2 % in 2020. The co-detection of methadone and benzodiazepines with opioids decreased over the study period (AOR 0.92, 95 % CI 0.91–0.92, p < .0001), ranging from 36.7 % in 2010 to 26.9 % in 2020.

Conclusion

Interventions are needed to target the persistently high use of benzodiazepines among patients in receipt of methadone due to their synergistic effects with opioids on respiratory depression, enhancing the risk of overdose. The growing use of cocaine among people in MMT also needs to be addressed.