A new nationally representative study has found that close to one in four young adults in Ireland consume multiple psychoactive substances within a short timeframe.
The study, ‘Polysubstance use in early adulthood and associated factors in the Republic of Ireland: An analysis of a nationally representative cohort,’ published in the journal Addiction, uses data from more than 4,600 participants in the Growing Up in Ireland (GUI) study, tracked from childhood into early adulthood.
Four classes of substance
The study examined substance use at age 20 years and identified four distinct groups through latent class analysis.
Approximately 33.8% of participants were categorised as ‘limited users’, marked by low‑risk alcohol consumption and minimal involvement with other substances.
A further 43.0% fell into the ‘alcohol, tobacco, and cannabis’ class, with higher rates of these substances and relatively low use of others.
Two polysubstance groups were identified. Around 16.2% of young adults regularly used alcohol, tobacco, cannabis, cocaine, and ecstasy.
Another 7% were classified as ‘heavy polysubstance users’, characterised by frequent and varied drug consumption, including ketamine and additional substances.
This group showed the highest likelihood of high‑risk or dependent alcohol use and repeated use of multiple illicit drugs.
Factors associated with higher‑risk use
The study also highlighted several individual, familial, and social factors associated with higher‑risk patterns.
Male participants were significantly more likely than females to belong to polysubstance classes.
Early alcohol use, particularly drinking before the age of 15 years, was strongly linked with later polysubstance involvement.
Family background featured prominently. Participants who reported parental alcohol or drug problems were more likely to be in polysubstance groups, as were those whose parents had lower levels of education.
Having friends who used cannabis at age 17 years was associated with a substantial increase in the odds of belonging to a polysubstance class by age 20 years.
Living arrangements and location were also relevant. Young adults living outside the parental home and those residing in Dublin were more likely to fall within heavier substance use categories.
International comparisons and policy considerations
The findings place Ireland’s 23.2% polysubstance prevalence at the higher end internationally. Comparable studies in the United States of America and Australia have reported prevalence rates between 6% and 15%.
The study notes policy implications, including the need for approaches that consider multiple substances simultaneously rather than addressing them individually.
Also highlighted was the need for strategies that delay alcohol initiation, support families, and reduce peer influence.
The authors refer to measures within Ireland’s Public Health (Alcohol) Act 2018 – such as minimum unit pricing and marketing restrictions – as representing progress, while stating that additional harm reduction and education initiatives will be required to address the complexities of polysubstance use.
This blog is based on an article by Dr Millar in the current edition of Drugnet available here.
