Clustering of substance use and sexual risk behaviour in adolescence: analysis of two cohort studies

Objectives: The authors aimed to examine whether changes in health risk behaviour rates alter the relationships between behaviours during adolescence, by comparing clustering of risk behaviours at different time points. Design: Comparison of two cohort studies, the Twenty-07 Study (‘earlier cohort’, surveyed in 1987 and 1990) and the 11-16/16+ Study (‘later cohort’, surveyed 1999 and 2003). Setting: Central Clydeside Conurbation around Glasgow City. Participants: Young people who participated in the Twenty-07 and 11-16/16+ studies at ages 15 and 18–19. Primary and secondary outcomes measures: The authors analysed data on risk behaviours in both early adolescence (started smoking prior to age 14, monthly drinking and ever used illicit drugs at age 15 and sexual intercourse prior to age 16) and late adolescence (age 18–19, current smoking, excessive drinking, ever used illicit drugs and multiple sexual partners) by gender and social class. Results: Drinking, illicit drug use and risky sexual behaviour (but not smoking) increased between the earlier and later cohort, especially among girls. The authors found strong associations between substance use and sexual risk behaviour during early and late adolescence, with few differences between cohorts, or by gender or social class. Adjusted ORs for associations between each substance and sexual risk behaviour were around 2.00. The only significant between-cohort difference was a stronger association between female early adolescent smoking and early sexual initiation in the later cohort. Also, relationships between illicit drug use and both early sexual initiation and multiple sexual partners in late adolescence were significantly stronger among girls than boys in the later cohort. Conclusions: Despite changes in rates, relationships between adolescent risk behaviours remain strong, irrespective of gender and social class. This indicates a need for improved risk behaviour prevention in young people, perhaps through a holistic approach, that addresses the broad shared determinants of various risk behaviours.