Home > Age at first substance use, persistence of cannabis use, and cannabis use disorder in Ireland.

Millar, Sean (2021) Age at first substance use, persistence of cannabis use, and cannabis use disorder in Ireland. Drugnet Ireland, Issue 79, Autumn 2021, pp. 22-23.

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Background and methods

There is ongoing debate regarding the relationships between early onset substance use and later use of other drugs. The common liability model states that a combination of risk factors places some people at increased risk of both early initiation and of subsequent progression to more serious and sustained drug abuse.1 Numerous studies have examined relationships between early onset drinking, tobacco, and cannabis use with later drug use. However, this research has tended to focus on a narrow 12–25-year-age range. In addition, fewer studies have explored factors associated with progression to ongoing, heavier, and problematic cannabis use among lifetime cannabis users. It is also unclear whether associations between younger age at substance use onset and cannabis use patterns are independent of other influential factors that may constitute an underlying vulnerability for heavier substance use and substance use disorders.

A 2021 Irish study2 determined the relationships between age at first use of alcohol, tobacco, and cannabis and the patterns of cannabis use, frequency of use, and whether age of substance use onset is related to having a cannabis use disorder (CUD). In this research, published in the journal BMC Public Health, data were analysed from Ireland’s 2010/11 and 2014/15 National Drug Prevalence Surveys, which recruited 5,134 and 7,005 individuals, respectively, aged 15 years or more, living in private households. Multinomial, linear, and binary logistic regression analyses were used to determine the relationships between age of substance use onset and patterns of cannabis use, frequency of use, and having a CUD.


When compared with former users, the odds of being a current cannabis user were found to be reduced by 11% (OR=0.89; 95% CI: 0.83–0.95) and 4% (OR=0.96; 95% CI: 0.92–1.00) for each year of delayed alcohol and cannabis use onset, respectively. Among current users, significant inverse linear relationships were noted, with increasing age of first use of tobacco (β=–0.547; p<0.001) and cannabis (β=–0.634; p<0.001) being associated with a decreased frequency of cannabis use within the last 30 days. The odds of having a CUD were found to be reduced by 14% (OR=0.86; 95% CI: 0.78–0.94) and 11% (OR=0.89; 95% CI: 0.82–0.98) for each year of delayed tobacco and cannabis use onset, respectively, in analyses which examined survey participants aged 15–34 years. 


The authors discussed that planning models based on the needs of the population are important for the successful implementation of treatment services and to adequately plan these services requires an understanding of the population in need of treatment. Findings from this study suggest that, in Ireland, prevention initiatives should prioritise younger adult cannabis users with a pattern of very early onset tobacco or cannabis use.

1   Van Leeuwen AP, Verhulst FC, Reijneveld SA, Vollebergh WAM, Ormel J and Huizink AC (2011) Can the gateway hypothesis, the common liability model and/or, the route of administration model predict initiation of cannabis use during adolescence? A survival analysis – the TRAILS study. J Adolesc Health, 48(1): 73–78. https://www.drugsandalcohol.ie/34674/

2  Millar SR, Mongan D, Smyth BP, Perry IJ and Galvin B (2021) Relationships between age at first substance use and persistence of cannabis use and cannabis use disorder. BMC Public Health, 21: 997.

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