Introduction.

The availability of drugs and its impact upon our society is undeniably a public concern; the question that remains is to what extent is the population affected. Different sources of information suggest that drug use in Mexico is increasing, especially among the adolescent population. As it has been thirty years since the first epidemiological study of drug use was conducted in Mexico in the 1970’s, this is an opportune moment to evaluate the problem by age cohort. This research addresses the question of whether changes in substance use have differentially affected the younger population in terms of the evolution of ages of onset and the socio-demographic determinants of lifetime consumption.

Method.

This study is a part of the World Mental Health Surveys Initiative from the WHO which was undertaken simultaneously in 30 countries. The target population was taken from uninstitutionalized persons with a fixed residence, between 18 and 65 years of age, and living in urban areas (as defined by more than 2500 inhabitants). The survey is based on a probabilistic, multistage design, stratified by six geographic areas at the national level. Eligible respondents were defined as persons, aged 18 to 65 at the time of the survey, who normally eat, sleep and prepare meals in the household and limited to those that speak Spanish. A total of 5826 individuals were interviewed with a weighted individual response rate of 76.6%. The computer assisted version of the World Mental Health Composite International Diagnostic Interview (WMH-CIDI)was administered. The interview length varied from a minimum of 20 minutes to a maximum of nine hours in four sessions. Fieldwork was carried out by 34 lay interviewers with prior experience in survey data collection and trained by professionals certified by the WHO in the use and training of the CIDI. Standard errors of the estimated prevalences were calculated by the Taylor linearization method using the SUDAAN 2002 statistical package. Kaplan Meir survival curves were generated for the ages of onset using the SAS 2001 software. Logistic regressions were performed to study the demographic correlates of substance use. Estimates of standard errors of odds ratio (ORs) from logistic regression coefficients were also obtained by SUDAAN, and 95% Confidence Intervals (CI) have been adjusted to design effects.

Results.

Alcohol is the most used substance with less variation by age; 86% of those interviewed report alcohol consumption at some time in their life. The prevalence of alcohol use is followed by tobacco use. Sixty percent of the population report having used tobacco, reaching the greatest proportion of the population in the 45 to 54 year old age group (63%). The non-medical use of drugs, including illicit drugs and legal drugs without a medical prescription, reaches 10% of the population. The illegal use of drugs, including the non-medical use of legal drugs and illicit drugs, in particular marijuana and cocaine, is more frequent among the young and prevalence diminishes with age. Beginning in adolescence, there is a growing prevalence of those reporting the use of these substances, stabilizing shortly before the age of 30. A discrete time survival analysis to estimate the variation in the lifetime prevalence by cohort showed variations in drug use by cohort for all the substances studied, even for alcohol consumption. In all cases, compared to the oldest cohort, the younger cohort are at greater risk of substance use and the greatest risks are concentrated always in the youngest cohort. The cohort differences in probability of substance use is greatest for cocaine, with increases of up to 100 times the risk for those between 18 and 29 years of age. Results of a logistic regression model demonstrate that age continues to be an important risk factor for non-prescription medical substance use, marijuana and cocaine, but not for alcohol and tobacco. For all substances, use is substantially lower for females as well as for the homemaker category of employment. There are no consistent differences for the other demographic variables across the five types of substances.

Discussion.

This report documents an increase in the risk for substance abuse problems among today’s youth, greater than the risk faced by their parents or grandparents at the same age. Use begins increasing during adolescence and stabilizes shortly before the age of 30. There are variations by type of drug such that marijuana has maintained an early age of onset in the different age cohorts while for the use of other substances new cases of onset are found after this age; the substance that shows the greatest proportion of new onset at later ages is cocaine. Even so, the risk of cocaine use is considerably greater in younger cohorts. Survival analysis confirms that compared to older cohorts, the younger have greater risk of substance use and these risks are particularly striking for cocaine use, with as much as 100 times the risk for those between 18 and 29 years of age. These findings coincide with those reported in previous studies in that alcohol and tobacco use surpass by far the use of other substances, with greater use of alcohol than tobacco and both above any other substance. The rate of tobacco and alcohol use is similar throughout the lifespan signifying that this is an endemic problem in our country. On the other hand, findings regarding the use of illegal drugs, in particular marijuana and cocaine, and non-prescription medical drugs show a preponderance of use in the young. These findings reflect the tendencies already reported in other studies. Marijuana use is not new, and has a long tradition throughout the country for which it is not surprising that these results show cases of consumption in all age groups and that the age of onset is similar in all age cohorts, around 17 years of age. However, the growth of marijuana use is reflected by greater lifetime prevalence in the young, three times greater among those now currently 18 to 29 years of age than those of the same age in the 1970’s. The use of cocaine before that decade was limited to isolated groups as a socially sophisticated diversion; there is a resurgence in the 1990’s when an important increase in use is reflected in all the available surveillance systems. This is reflected in our results by the lower exposure to this drug in the older cohorts. While the risk of marijuana use is 16 times lower in the older cohort than the younger, the risk of cocaine use is 100 times lower in the older cohort than the younger. Our findings suggest that age continues to be an important risk factor for the use of illegal drugs and medical drugs without a prescription, but not for alcohol or tobacco. For all substances, use is lower for females as well as for homemakers indicating that double standards between the genders are still applied. For alcohol there are slightly lower risks for those with lesser educational attainment. This is consistent with other studies which have documented that alcohol consumption increases with buying power which is in turn associated with increased education. These results suggest the need to undertake further research which would allow us a more in depth understanding of the role that social position, including marital status, plays in substance use and abuse.

Conclusions.

These findings support the hypothesis that the younger generation of today has a greater risk of substance use when compared to their parents when they were young. This point out to the need of increasing actions aimed at reducing the negative impact of this phenomena upon health and society.

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