Background Evidence on the role of cannabis as a gateway drug is inconsistent. We characterise patterns of cannabis use among UK teenagers aged 13–18 years, and assess their influence on problematic substance use at age 21 years.
Methods We used longitudinal latent class analysis to derive trajectories of cannabis use from self-report measures in a UK birth cohort. We investigated (1) factors associated with latent class membership and (2) whether latent class membership predicted subsequent nicotine dependence, harmful alcohol use and recent use of other illicit drugs at age 21 years.
Results 5315 adolescents had three or more measures of cannabis use from age 13 to 18 years. Cannabis use patterns were captured as four latent classes corresponding to ‘non-users’ (80.1%), ‘late-onset occasional’ (14.2%), ‘early-onset occasional’ (2.3%) and ‘regular’ users (3.4%). Sex, mother's substance use, and child's tobacco use, alcohol consumption and conduct problems were strongly associated with cannabis use. At age 21 years, compared with the non-user class, late-onset occasional, early-onset occasional and regular cannabis user classes had higher odds of nicotine dependence (OR=3.5, 95% CI 0.7 to 17.9; OR=12.1, 95% CI 1.0 to 150.3; and OR=37.2, 95% CI 9.5 to 144.8, respectively); harmful alcohol consumption (OR=2.6, 95% CI 1.5 to 4.3; OR=5.0, 95% CI 2.1 to 12.1; and OR=2.6, 95% CI 1.0 to 7.1, respectively); and other illicit drug use (OR=22.7, 95% CI 11.3 to 45.7; OR=15.9, 95% CI 3.9 to 64.4; and OR=47.9, 95% CI 47.9 to 337.0, respectively).
Conclusions One-fifth of the adolescents in our sample followed a pattern of occasional or regular cannabis use, and these young people were more likely to progress to harmful substance use behaviours in early adulthood.
- LONGITUDINAL STUDIES
- DRUG MISUSE
- ADOLESCENTS CG
- Cohort studies
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Contributors MT conducted the literature review and drafted and revised the paper. SMC cleaned and analysed the data and revised the draft paper. MRM revised the draft paper. JM wrote the statistical analysis plan and revised the draft paper. MH revised the draft paper. JH assisted in analysis of the data and revised the draft paper.
Funding The UK Medical Research Council and the Wellcome Trust (grant ref.: 1002215/2/13/2) and the University of Bristol provide core support for ALSPAC. This work was supported by the Centre for the Development and Evaluation of Complex Interventions for Public Health Improvement (DECIPHer), which receives funding from the British Heart Foundation, Cancer Research UK, Economic and Social Research Council (RES-590-28-0005), Medical Research Council, the Welsh Assembly Government and the Wellcome Trust (WT087640MA), under the auspices of the UK Clinical Research Collaboration (MH). JH is supported by the UK Medical Research Council and Alcohol Research UK (MR/L022206/1). MT is supported by the Wellcome Trust (grant number: 097088/Z/11/Z).
Disclaimer The funding sources had no involvement in the study design, the collection, analysis and interpretation of the data, writing the report or in the decision to submit the manuscript for publication. This publication is the work of the authors who will serve as guarantors for the contents of the paper.
Competing interests None declared.
Ethics approval Ethical approval for this specific analysis was not required. Ethical approval has previously been obtained for the ALSPAC birth cohort form the ALSPAC Law and Ethics Committee and the Local Research Ethics Committees.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement The authors are unable to make the minimal data set publicly available as requests need to be submitted to a named access committee. Raw data for this submission will be made available on request to the ALSPAC executive committee (firstname.lastname@example.org). The ALSPAC data management plan (available here: http://www.bristol.ac.uk/alspac/researchers/dataaccess/) describes in detail the policy regarding data sharing which is through a system of managed open access.
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