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

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%).

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.

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.