Factors Associated With Cocaine Use at 17 and 20 Years Old: A Longitudinal Analysis of a Nationally Representative Cohort.

PURPOSE: Despite growing concerns about trends in cocaine use, there is a shortage of longitudinal research that prospectively examines risk and protective factors associated with cocaine initiation and use in general youth populations. This study addresses this gap.

METHODS

Growing Up in Ireland is a nationally representative cohort. Individual, family, and socio-environmental exposures associated with incident past-year cocaine use at ages 17 (N = 5965) and 20 (n = 4549) were assessed with survey-weighted logistic regression using generalised estimating equations. Prevalent past-year cocaine use at 20 (N = 4679) was analysed using generalised estimating equations complemented by gradient-boosted decision trees and Shapley explanations.

RESULTS

221 (3.7%) self-reported cocaine use at 17 and 1072 (22.9%) at 20. Alcohol use at 14 or younger was associated with eight times the odds of cocaine use at 17 (aOR 8.0, 95% CI 1.7-37.3) and 19 times at 20 (aOR 19.2, 95% CI 8.6-43.2). Peer cannabis use was associated with 7 times the odds of cocaine use at 17 (aOR 7.3, 95% CI 2.9-18.3) and double at 20 (aOR 2.4, 95% CI 1.8-3.2). Growing up in a neighbourhood where substance use was common doubled the odds of cocaine use at 17 (aOR 2.4, 95% CI 1.3-4.4). Shapley explanations revealed individual-specific positive or negative impacts of exposures.

DISCUSSION: Cocaine use among 20-year-olds in Ireland is higher than reported internationally, and increases sharply between the ages of 17 and 20, suggesting a need for interventions targeting this age group. However, associations with early adolescent factors suggest that early interventions may also be important.