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)

Source: Hanrahan et al. (2025)

Trends in problematic opioid use in Ireland over time

Data for the prevalence of problematic opioid use for the years 2020, 2021, 2022 are additionally presented to provide information on changes in trends over time (see Table 2). The overall estimated number of problematic opioid users remained stable between 2020 and 2022, as indicated by overlapping 95% CIs. However, the number of problematic opioid users aged 15–24 years decreased, from 685 (95% CI: 673–779) in 2020 to 527 (95% CI: 524–627) in 2022, which was a statistically significant decrease. No notable changes in the other age groups were observed.

Table 2: Comparison of estimated number of problematic opioid users over time (2020–2022), by age group

Source: Hanrahan et al. (2025)

This study represents the third national CRC study in Ireland to utilise four data sources: clinics, GPs, prisons, and the Probation Service. When comparing summary findings from previous studies with those shown in this report (Table 3), a stable overall estimated number of problematic opioid users was observed in Ireland between 2014 and 2022. There has been a slight decrease in the estimated number of problematic opioid users in Co Dublin; the estimated number of problematic opioid users living in the rest of Ireland outside of Co Dublin has increased from 5,530 (95% CI: 5,406–8,023) in 2014 to 8,360
(95% CI: 8,189–10,346) in 2022. However, these differences were not statistically significant based on overlapping 95% CIs. These data also show that there was no significant change in the proportion of male or female problematic opioid users during this period. Notably, there has been a significant decrease in the estimated number of problematic opioid users aged 15–24 years and aged 25–34 years (Figures 1 and 2), accompanied by a significant increase in the estimated number of problematic opioid users aged 35–64 years between 2011 and 2022 (Figure 3).

Table 3: Comparison of the estimated number of problematic opioid users in Ireland, 2014, 2019, and 2022

Source: Hanrahan et al. (2025)

Figure 1: Comparison of estimated rate of problematic opioid users per 1,000 population over time
(2011–2022), 15–24-year-olds

Source: Hanrahan et al. (2025)

Figure 2: Comparison of estimated rate of problematic opioid users per 1,000 population over time
(2011–2022), 25–34-year-olds

Source: Hanrahan et al. (2025)

Figure 3: Comparison of estimated rate of problematic opioid users per 1,000 population over time
(2011–2022), 35–64-year-olds

Source: Hanrahan et al. (2025)

Discussion

Comparing estimates of problematic opioid use in Ireland with those from other European Union (EU) member states is challenging, due to differences in methodologies and study years. However, the EUDA reports that national rates of high-risk opioid use in the EU range from fewer than 1 to nearly 10 users per 1,000 population aged 15–64 years.⁸ Based on the European Drug Report 2022: Trends and Developments and data from this study, Ireland would rank sixth highest in the EU for problematic opioid use according to upper 95% CI estimates.⁸ EU countries with higher estimates include Denmark (4.0–9.6 per 1,000 population), Finland (6.9–8.6 per 1,000 population), Italy (7.2–7.9 per 1,000 population), Latvia (4.6–7.0 per 1,000 population), and Portugal (3.0–7.0 per 1,000 population).⁸ The United Kingdom (UK) also has high estimates, with rates of 8.1–8.6 per 1,000 population reported in 2018.⁹ Notably, findings align with trends in other EU countries, where the majority of opioid users are male, and an ageing cohort effect is observed.⁸ This may reflect improved harm reduction services that enable problematic opioid users to live longer. Additionally, changes in drug use behaviours are evident, with problematic opioid users initiating opioid use later in life, reducing injection practices, using opioids less frequently, and seeking treatment at later stages.¹⁰

In conclusion, the results from this study indicate that the overall number of problematic opioid users in Ireland remained stable from 2020 to 2022, but with a significant decrease observed in the 15–24-year-old age group. This decrease is a positive development, given the harmful and addictive nature of opioids. Nevertheless, opioid use prevalence estimates in Ireland remain high. Ongoing research in this area will be crucial for effective service planning and also to enable policy-makers to evaluate the impact of strategies aimed at reducing drug-related harms. Further targeted interventions may be needed in order to enhance the response to opioid misuse in Ireland, thus leading to better outcomes for affected individuals and communities.

An electronic copy of the report is available from the National Drugs Library at: www.drugsandalcohol.ie/42700 

1. European Monitoring Centre for Drugs and Drug Addiction (2013) PDU (problem drug use) revision summary. Luxembourg: Publications Office of the European Union, 2013. Available from:
   https://www.drugsandalcohol.ie/27693/1/att_218205_EN_PDU%20revision.pdf
2. Comiskey C (1998) Estimating the prevalence of opiate drug use in Dublin, Ireland during 1996. Dublin: Department of Health and Children, 1998. Available from: https://www.drugsandalcohol.ie/5080/
3. Kelly A, Carvalho M and Teljeur C (2003) Prevalence of opiate use in Ireland 2000–2001: a 3-source capture recapture study. Dublin: Stationery Office. Available from: https://www.drugsandalcohol.ie/12695/
4. Kelly A, Teljeur C and Carvalho M (2009) Prevalence of opiate use in Ireland 2006: a 3-source capture recapture study. Dublin: Stationery Office. Available from: https://www.drugsandalcohol.ie/12695/
5. Hay G, Jaddoa A, Oyston J, Webster J, Van Hout MC and Rael dos Santos A (2017) Estimating the prevalence of problematic opiate use in Ireland using indirect statistical methods. Dublin: National Advisory Committee on Drugs and Alcohol. Available from: https://www.drugsandalcohol.ie/27233/
6. Hanrahan MT, Millar SR, Phillips KP, Reed TE, Mongan D and Perry IJ (2022) Problematic opioid use in Ireland, 2015–2019. Dublin: Health Research Board. Available from: www.drugsandalcohol.ie/42700
7. Hanrahan MT, Millar SR, Mongan D, Lyons S and Galvin B Prevalence of problematic opioid use in Ireland, 2020–2022. Dublin: Health Research Board, 2025. Available from: www.drugsandalcohol.ie/42700
8. European Monitoring Centre for Drugs and Drug Addiction. European Drug Report 2022: Trends and Developments. Luxembourg: Publications Office of the European Union, 2022. Available from:
   https://www.euda.europa.eu/publications/edr/trends-developments/2022_en
9. Public Health England, Home Office, Welsh Government, The Scottish Government, Public Health Wales, Northern Ireland. Department of Health. United Kingdom drug situation: Focal Point annual report 2019. London: Gov.UK, 2020. Available from: https://www.drugsandalcohol.ie/32563/
10. Carew AM and Comiskey C Rising incidence of ageing opioid users within the EU wide treatment demand indicator; The Irish opioid epidemic from 1996 to 2014. Drug Alcohol Depend 2018;192:329-37. Available from: https://www.drugsandalcohol.ie/29783/

Since 2006, the Growing Up in Ireland (GUI) national longitudinal study of children and young people has followed a cohort of children born in 1998. Five waves of interviews have been conducted with this cohort when they were aged 9, 13, 17–18, 20, and 25 years. This article presents findings on drug use from 3,380 interviews with the 25-year-old participants, which were conducted in 2023–24.¹

Any drug use

Figure 1 shows the prevalence of illicit drug use among 25-year-olds in the GUI study. Cannabis was the most prevalent drug, with 56.6% of respondents stating that they had ever tried it. Just over one-fifth (21.4%) of 25-year-olds reported ever having tried cocaine, and cocaine usage in the last year was more common for men (24.3%) than for women (18.6%). The other most commonly reported drugs were ecstasy (10.7%), ketamine (9.7%), and magic mushrooms (6.9%).

Current cannabis use

One in seven (14.2%) respondents said they were current cannabis users, and more men (16.1%) than women (12.3%) indicated current cannabis use (see Figure 2). Those who had at least an NFQ Level 7 or equivalent qualification and those who did not reported comparable rates of cannabis use (14.3% of those with such a qualification compared with 14.0% of those without).

Figure 1: Lifetime illicit drug use among 25-year-olds in Ireland, 2023–24

Source: GUI Ireland (2025)

LSD: lysergic acid diethylamide.

Figure 2: Percentage of 25-year-olds who indicated current cannabis use, 2023–24

Source: GUI Ireland (2025)

1. Central Statistics Office (2025) Growing Up in Ireland: Cohort ’98 at age 25 main results. Cork: Central Statistics Office. Available from: https://www.drugsandalcohol.ie/42586/

The first Health Behaviour in School-aged Children (HBSC) study was conducted in Ireland in 1998 and has been repeated every 4 years ever since. In 2022, Ireland participated in the HBSC study for the seventh time. The survey included a representative sample of 9,071 children drawn from primary and post-primary schools across Ireland; 191 schools participated. Data were collected on general health, smoking, use of alcohol and other substances, food and dietary behaviour, exercise and physical activity, self-care, injuries, bullying, and sexual health behaviours. The main results were published in 2025.¹ This article describes results pertaining to the use of cannabis and makes comparisons with previous HBSC studies.

Cannabis use in the last year

Overall, 6.5% of 10–17-year-olds said that they had used cannabis in the last year. The prevalence of cannabis use increased with age, and a higher percentage of boys aged 10–14 years reported using cannabis compared with girls (see Table 1). Almost 13% of boys and 13.4% of girls aged 15–17 years reported having used cannabis in the last year.

Table 1: Percentage of 10–17-year-olds reporting cannabis use in the last year, by sex and age group, 2022

Source: HBSC Ireland (2025)

Figure 1: Percentage of 10–17-year-olds who reported cannabis use in the last 12 months, overall and by sex, from 1998 to 2022

Source: HBSC Ireland (2022)Trends in cannabis use among Irish school-aged children, 1998–2022

Although a higher percentage of 10–17-year-olds reported having used cannabis in 2018 compared with the 2014 HBSC study (see Figure 1), there has been a steady decrease in the lifetime use of cannabis among school-aged children since 1998, with data from 2022 indicating an 82.1% reduction among boys and a 28.9% reduction among girls.

It is worth noting that these findings are from the first HBSC Ireland study conducted since the start of the COVID-19 pandemic. Data were collected during a time when schools had recently reopened and when young people were readjusting following long periods of school closures and remote learning. Consequently, these findings should be interpreted with this specific historical time frame in mind, considering the impacts of recent COVID-19 pandemic measures on young people’s lives.

1. Gavin A, Kolto A, Lunney L, et al. (2024) The Irish Health Behaviour in School-aged Children (HBSC) Study 2022. Galway: Department of Health and University of Galway. Available from: https://www.drugsandalcohol.ie/40947/

Cannabis remains the most widely used illicit substance among adolescents in Ireland, with new research shedding light on the factors that influence its use. A 2021 survey involving over 4,400 students aged 15–16 years in North Dublin, Cavan, and Monaghan revealed that 7.3% reported using cannabis in the past month. The study, part of the Planet Youth initiative based on the Icelandic Prevention Model, identified individual, familial, and peer-related factors related to cannabis use.

In this research, which has been published in the Irish Journal of Psychological Medicine, peer cannabis use was found to increase the odds of a young person’s cannabis use by over 10 times.¹ Perceived parental ambivalence and peer pressure also significantly elevated the likelihood of use. Moreover, adolescents who viewed cannabis as non-harmful – or who used alcohol, cigarettes, or e-cigarettes – were more likely to be cannabis users. Protective factors against adolescent cannabis use included strong parental disapproval, high levels of parental supervision, and the perception that cannabis use is harmful.

The authors propose that the findings have important implications for public health policy and highlight the need for targeted prevention strategies that address modifiable risk factors, such as peer influence and parental attitudes. They suggest that increased public awareness campaigns that clarify the risks associated with adolescent cannabis use, particularly in the context of growing social acceptance and legalisation debates, are urgently needed.

1. O’Dowd TM, Fleury R, Power E, et al. (2025) Risk and protective factors for cannabis use in adolescence: a population-based survey in schools. Ir J Psychol Med, 42, (1) pp. 6–14.