Background

In 2023, the Health Research Board (HRB) partnered with Trinity College Dublin to examine the alcohol- and drug-related data collected in the nationally representative, longitudinal Growing Up in Ireland (GUI) study. A series of publications have ensued as a result of this collaboration.1-4 The most recent of these examined the association between age of alcohol initiation and hazardous alcohol use during adolescence with alcohol, tobacco, cannabis, and other drug use during early adulthood.5

Methods

Using logistic regression methodology (bivariable and multivariable logistic regression models), the study used GUI data from Wave 1 (when participants were aged 9 years), Wave 2 (when participants were aged 13 years), and Wave 3 (when participants were aged 17 years) and examined the association between age of alcohol initiation and reports of hazardous drinking patterns (using the Alcohol Use Disorders Identification Test (AUDIT) scores) at Wave 3 with high-risk alcohol (AUDIT score >15), tobacco, cannabis, and other drug6 use at Wave 4 (when participants were aged 20 years).

Results

Of the 4,554 participants who completed all 4 waves of the survey, over one-quarter (27%) had their first alcoholic drink at age 14 years or younger and by age 17 years, 6% had an AUDIT score of 15 or higher, indicating high-risk drinking patterns; by age 20 years (Wave 4), this had increased to 14% of participants. Over one-third were smokers at age 20 years (38%), almost one-quarter were cannabis users (24%), and 28% had used other drugs in the past year.  

Bivariable regression analysis

Age of alcohol initiation

An examination of age of alcohol initiation revealed that delaying alcohol use was associated with lower rates of high-risk alcohol, tobacco, cannabis, or other drug use at age 20 years, relative to those who had their first alcoholic drink at age 14 years or younger. Conversely, early alcohol initiation was positively associated with substance use at age 20 years.

AUDIT scores at age 17 years

Those with ‘increasing risk’ alcohol use (an AUDIT score of between 8 and 15) at age 17 years had a fourfold increase in the odds of high-risk alcohol use at age 20 years, while those whose alcohol use was high risk (AUDIT score >15) at age 17 years had a 14-fold increase in the odds of continued high-risk alcohol use at age 20 years relative to adolescents who had been classified as low risk. In addition, high AUDIT scores at age 17 years doubled the odds of other drug use at age 20 years.

Multivariable regression analyses

Age of alcohol initiation

Following the addition of exposures and covariates, multivariable analyses continued to show the association between delayed alcohol use and reduced odds of high-risk alcohol use at age 20 years, although effect sizes were reduced. Delayed alcohol initiation also remained associated with reduced odds of cannabis and tobacco use at age 20 years.

AUDIT scores at age 17 years

High-risk alcohol use at age 17 years remained strongly associated with cannabis use at age 20 years, although it was not statistically significant. It also doubled the odds of tobacco use at age 20 years and was associated with an 11-fold increase in the odds of continued high-risk alcohol use at age 20 years.

Additional analyses

Additional analyses examining factors associated with substance use at age 20 years using survey-weighted multivariable generalised estimating equations regression models indicated that male sex doubled the odds of cannabis use and was associated with a 40% increase in the odds of other drug use.

Higher externalising scores (indicating a higher likelihood of hyperactivity, impulsivity, and aggression) were associated with a 50% increase in the odds of both tobacco use and high-risk alcohol use. Lower parental monitoring was associated with a 30% increase in the odds of cannabis use and a 40% increase in the odds of tobacco use. Those with friends who used cannabis at age 17 years had a fourfold increase in the odds of cannabis use and a threefold increase in the odds of other drug use.

Conclusions

Adjusted modelling analysis consistently showed that age of alcohol initiation and risky alcohol use during adolescence independently predict high-risk alcohol use, tobacco use, cannabis use, and other drug use in early adulthood. These findings add to the mounting conclusive evidence of the risks associated with alcohol use in children, especially early and risky alcohol use. Urgent public health measures to address this are required in order to prevent the escalation to more serious substance use in adulthood.

1    Mongan D, Millar S, Brennan MM, et al. (2025) Longitudinal associations between childhood adversity and alcohol use behaviours in early adulthood: examining the mediating roles of parental and peer relationships. Child Abuse Negl, 161: 107302. Available from: https://www.drugsandalcohol.ie/42645/

2    Mongan D, Millar S, Brennan M, et al. (2025) Associations and mediating factors between adverse childhood experiences and substance use behaviours in early adulthood: a population-based longitudinal study. Addict Behav, 161: 108194. Available from: https://www.drugsandalcohol.ie/42204/

3    Brennan M, Cavallaro M, Mongan D, et al. (2025) Factors associated with cocaine use at 17 and 20 years old: a longitudinal analysis of a nationally representative cohort. J Adolesc Health, 76: 488–498. Available from: https://www.drugsandalcohol.ie/42555/

4    Brennan M, Corrigan C, Mongan D, et al. (2024) Predictors and outcomes of adolescent alcohol and drug use: a scoping review. Eur J Public Health, 34. Available from: https://www.drugsandalcohol.ie/42212/

5    Brennan MM, Mongan D, Doyle A, et al. (2025) Early and risky adolescent alcohol use independently predict alcohol, tobacco, cannabis and other drug use in early adulthood in Ireland: a longitudinal analysis of a nationally representative cohort. BMC Public Health , 25: 1129. Available from: https://www.drugsandalcohol.ie/42914/

6    Cocaine, ecstasy, ketamine, amphetamines, poppers, lysergic acid diethylamide (LSD), magic mushrooms, crack, or the misuse of prescription drugs.