Trends in the detection and co-detection of drugs in a population attending opioid agonist treatment: 2010 to 2020

Background

Opioids remain a leading cause of drug-related mortality in Ireland, commonly in combination with other substances. While opioid agonist treatment is protective and reduces a person’s risk of death, many people continue to use non-prescribed substances ‘on top’ of their OAT medication which is a contributing factor to the discontinuation of treatment. The extent of polydrug use among people attending OAT has received little research attention. People attending opioid agonist treatment (OAT) in Ireland undergo regular urine drug screenings , allowing for an assessment of the detection and co-detection of a number of licit and illicit drugs in this high risk group.

The aim of this study is to examine trends in the detection and co-detection of alcohol, benzodiazepines, methadone, opiates, cocaine, cannabis, and amphetamines in a population attending OAT from 2010 to 2020.

Methods 

We used a repeated cross sectional study design, with anonymized individual sample level urine immunoassay drug screening data from the National Drug Treatment Centre (NDTC) laboratory. We present annual weighted sample positivity rates for alcohol, amphetamines, benzodiazepines, cannabis, methadone, cocaine and heroin. Mixed logistic regression models were employed to evaluate time trends in positive screening of each substance, while accounting for repeated samples per person. Adjusted odd ratios for age class and time are presented.

Results

A total of 1967 people  (223,241 samples) were included in the study. The mean age increased from 34.6 years in 2010 to 39.9 years in 2020. The detection of 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) increased over time. In contrast, we observed decreasing trends in the detection of alcohol (AOR 0.96, 95% CI 0.95 - 0.97, p <.0001) and opiates (AOR 0.91, 95% CI 0.9 - 0.92, p <.0001). Aside from alcohol and amphetamines, all substances were more likely to be detected in younger age groups (<36 years) vs older groups.

With a 69% average annual weighted positivity rate, co-detection of methadone with benzodiazepines was common. Co-detection of cocaine, benzodiazepines and methadone increased over the study period (AOR 1.24, 95% CI 1.23 - 1.25, p <.0001), reaching 29% weighted positivity rate in 2020.

Conclusion

Urine drug screening data can provide invaluable insight on substance/poly-substance use in a high risk population such as people attending OAT. Continued monitoring of poly-substance use, especially in more susceptible younger drug users is warranted. Beyond immunoassay, more comprehensive systematic testing could inform on emergence of new substance or patterns of use in near real-time.