Home > New estimates of problematic opioid use in Ireland, 2020–2022.

Millar, Seán ORCID: https://orcid.org/0000-0003-4453-8446 (2025) New estimates of problematic opioid use in Ireland, 2020–2022. Drugnet Ireland, Issue 92, Autumn 2025, Supplement, pp. 2-7.

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Background
Problematic opioid use is a significant problem in Ireland and across the world. However, measuring the prevalence of opioid use is challenging. Given the nature of this population, a simple head count is not feasible and general population surveys are known to be ineffective at capturing this ‘hidden’ population. Because people who use drugs fear stigmatisation and are often marginalised in society, the European Union Drugs Agency (EUDA) recommends the use of indirect approaches, such as the capture-recapture (CRC) method, to estimate the prevalence of problematic (high-risk) drug users.1

To date, one regional and four national CRC studies have been conducted in Ireland to estimate the prevalence of problematic opioid use. These studies provided estimates for the years 1996, 2000–01, 2006, 2011–2014, and 2015–2019.2,3,4,5,6 The 1996 regional study examined opioid use in Dublin only and used three data sources: the Health Service Executive (HSE) Central Treatment List (CTL), Hospital In-Patient Enquiry (HIPE) scheme data from four Dublin hospitals, and the An Garda Síochána arrest database. The 2000–01 and 2006 studies were three-source CRC studies that used national data from the CTL, the HIPE scheme and the An Garda Síochána PULSE (Police Using Leading Systems Effectively) database. The 2011–2014 and 2015–2019 studies both used four national data sources: the CTL data were divided into three sources (treatment clinics, general practitioners (GPs), and prison data), and the Probation Service was the fourth data source. In 2020, the Health Research Board (HRB) awarded a contract to the School of Public Health at University College Cork to conduct a fifth study on the prevalence of opioid use in the Republic of Ireland for the years 2020–2022. The methodology and main findings from this study are discussed below.7

Methods
Data on opioid use for the years 2020–2022 were collected from four sources: treatment clinics, general practitioners (GPs), the Irish Prison Service, and the Probation Service. Employing the CRC method, Poisson log-linear models were applied to the overlap data to find the model with the best fit to estimate the hidden population not identified by any of the data sources. Source-by-source interaction terms were tested by adding them to the base model in all possible combinations. The best model for estimating the size of the hidden population was determined by comparing the deviance to the chi-squared distribution and the Akaike information criterion (AIC) value. The simplest model with the lowest AIC value that provided a credible estimate was used.

Results
Table 1 presents a summary of the study’s main results, stratified by Co Dublin versus the rest of Ireland, as well as by age group and sex. In 2022, it was estimated that there were approximately 19,460 individuals in Ireland with problematic opioid use (95% confidence interval (CI): 19,348–23,158), which equates to a prevalence rate of 5.79 per 1,000 population (95% CI: 5.76–6.89). A significant majority of these individuals were male (67.9%), and more than two-thirds (75.3%) fell within the older age group of 35–64-year-olds. There were an estimated 11,100 problematic opioid users (95% CI: 10,684–13,761) in Co Dublin in 2022, reflecting a rate more than three times higher than that in the rest of Ireland (11.17 per 1,000 population (95% CI: 10.75–13.85), compared with 3.53 per 1,000 population (95% CI: 3.46–4.37).

Table 1: Summary of prevalence estimates of problematic opioid use (2022)