Age of Onset, Current Use of Alcohol, Tobacco or Marijuana and Current Polysubstance Use Among Male and Female Mexican Students.

Aims: This study aimed to examine alcohol, tobacco or marijuana use onset and associations between age of onset and current use, and between age of onset and current polysubstance use among a sample of Mexican young people aged 17-20 years.

Methods: Alcohol, tobacco, marijuana and other substance use were identified in a 2012 cross-sectional survey of male and female students entering first year university in Mexico City. Chi-square tests and logistic regression models examined associations between gender, age of onset, order of onset, family substance use and current polysubstance use among 22,224 students.

Results: The largest proportions of males and females initiated alcohol at age 15, tobacco at ages 15-16 and marijuana at ages 16-17. Earlier alcohol and tobacco initiation was associated with past 30-day use of the same substance. Gender differences in alcohol and tobacco use were small but males were significantly more likely than females to use marijuana and be polysubstance users. Family substance use was associated with earlier onset. There was a significant association between the earliest age of any of the three substances and current polysubstance use.

Conclusions: A number of contextual and cultural factors in Mexico may be contributing to early onset, continued use and polysubstance use and deserve attention in research and by prevention programs.