title: [Onset of alcohol and tobacco use and transition to other drug use among students from Morelos, Mexico].
abstract: OBJECTIVE
  To estimate the cumulative probability of occurrence of first use of alcohol and tobacco, and the risk of transition to illegal drugs (marijuana, cocaine, and heroine, among others), in adolescents and young adults, in Morelos State, Mexico.
  
  
  METHODS
  A cross-sectional study was conducted during schoolyear 1998-1999, among 13 293 students aged 11-24 years, selected from public schools by probabilistic multistage sampling. Data were collected on sociodemographic, health status, and substance abuse variables, using a validated self-applied questionnaire. Data were restructured to assemble a synthetic cohort for discrete time survival analysis. Associations were assessed with hazard rates and 95% confidence intervals obtained by means of multivariate Cox regression models.
  
  
  RESULTS
  Sixty percent of males started drinking alcohol at 17 years of age, and smoking tobacco at 18 years of age, on average. Women started using alcohol and tobacco one year after men. Utilization of illicit drugs occurred at 19 years of age on average in 5% of women and 13% of men. Nine out of every 100 illicit drug users started directly using illicit drugs without previous use of alcohol and/or tobacco. In general, alcohol or tobacco users were at greater risk of starting drug use than nonusers (RR=6.72; 95 % confidence interval [CI]=4.13-10.93).
  
  
  CONCLUSIONS
  Study findings suggest that interventions to decrease drug abuse should go together with efforts to delay initiation of alcohol and tobacco use. The innovative method used in this study yields epidemiologic evidence relating early use of alcohol and tobacco with initiation of illegal drugs in Mexican students.
authors.affiliation: Instituto de Seguridad y Servicios Sociales de los Trabajadores del Estado, Delegación Estatal Puebla, Puebla, Puebla, México.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Herrera-Vázquez
authors.forename: Fernando A
authors.initials: FA
authors.lastname: Wagner
authors.forename: Eduardo
authors.initials: E
authors.lastname: Velasco-Mondragón
authors.forename: Guilherme
authors.initials: G
authors.lastname: Borges
authors.forename: Eduardo
authors.initials: E
authors.lastname: Lazcano-Ponce
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000428:Alcohol Drinking / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008297:Male; D008800:Mexico / Q000453:epidemiology; D012907:Smoking / Q000453:epidemiology*; D019966:Substance-Related Disorders / Q000453:epidemiology; D014505:Urban Population