Male–female differences in the risk of progression from first use to dependence upon cannabis, cocaine, and alcohol
Introduction
Epidemiologists commonly report male–female differences in the prevalence of drug use and dependence (e.g., see Anthony et al., 1994, Vega et al., 2002, SAMHSA, 2003). It has been suggested that there may be male–female differences in the incidence (or ‘risk’) of becoming dependent, or in persistence of dependence once the syndrome develops. However, to date, analyses focused upon male–female differences in prevalence of drug dependence have tended to ignore this distinction between ‘risk’ and persistence. This paper focuses on the first issue—namely, that male–female differences can be seen in the instantaneous risk or hazard of becoming dependent once drug use starts.
Males tend to be more likely than females to have developed dependence upon alcohol and other controlled substances and inhalants; this does not appear to be the case for tobacco (Anthony et al., 1994, Warner et al., 1995). In lifetime (retrospective) analyses restricted to users of cannabis and alcohol, males were more likely than females to have developed dependence upon these two drugs. Nonetheless, minimal differences were observed between male and female cocaine users with respect to the cumulative occurrence of developing cocaine dependence between first use and date of dependence assessment (i.e., “cumulative” to that date without regard to elapsed time; Anthony et al., 1994).
In a recent report of epidemiological evidence from the United States (US), our research group estimated both cumulative occurrence and instantaneous risk of first drug use and first progression to dependence upon cannabis, cocaine, and alcohol, with an age-specific approach that considers age of first use and the time course to development of dependence upon these drugs (Wagner and Anthony, 2002a). There, we reported that estimated peak values for becoming dependent upon alcohol and cannabis were found at age 17–18, while peak values for becoming cocaine dependent were found at ages 23–25. Once drug use started, cocaine dependence emerged earlier and more explosively than dependence upon cannabis and alcohol, with an estimated 5–6% of cocaine users becoming cocaine dependent in the first year of use, as compared to no more than roughly 1% of cannabis and alcohol users developing dependence in the initial year after onset of use of these drugs.
A natural extension of the previous work includes descriptive analyses of male–female differences with regard to the risk of drug dependence. Here, our goal is not to explain or account for male–female differences, which we cannot accomplish in this particular survey. Rather, we seek to offer new evidence on possible male–female differences with specific focus upon elapsed time from first use to onset of dependence upon cannabis, cocaine, and alcohol among users of these drugs, based on novel analyses of survey data. If there are no such differences, then the already published estimates and survival curve estimates for all persons will serve well until estimates from new surveys are published. However, we launched this investigation with an expectation that the risks of becoming dependent might be different for these two subgroups of the population—i.e., male users versus female users. If so, future more detailed studies of observed male–female differences can be motivated by the new evidence, including analyses of more recently gathered data to see whether this study's findings can be replicated by other research teams.
Section snippets
Methods
Methods used in this study have been described elsewhere in more detail (Kessler et al., 1994, Anthony et al., 1994, Warner et al., 1995, Wagner and Anthony, 2002a). Briefly, we analyzed data from the National Comorbidity Survey (NCS), which are based upon a representative sample of all non-institutionalized people living in the US, 15–54 years old, in 1990–1992. In contrast to prior reports on prevalence of use, this work offers insights into male–female differences in the instantaneous risk
Results
Fig. 1 depicts estimates for the risk of first cannabis, cocaine, and alcohol use, as well as the estimated cumulative probability of first use of each of these drugs, by age. Peak estimates for the risk of cannabis and alcohol first use were observed between ages 18 and 19, and around 21–22 years for cocaine. In general, the risk of first use shows a male excess. The estimated risk of first alcohol use is greater than that for cannabis and cocaine, at each age.
Among users, for males and
Discussion
In a departure from most prior research on alcohol and drug dependence, which has been focused upon the prevalence of being drug dependent, we launched this study to explore male–female differences in the risk of becoming drug dependent once drug use begins, and to check whether previously published risk estimates hold equally well for males and females. We have found that, over time, once drug use starts, there is an accumulation of cases of cannabis dependence and alcohol dependence such that
Acknowledgements
The authors wish to acknowledge valuable comments from Dr. Carla L. Storr to a prior version of the present manuscript.
The NCS is a collaborative epidemiologic investigation of the prevalence, causes, and consequences of psychiatric morbidity and comorbidity in the United States supported by grant RO1 MH46376 from the US Alcohol, Drug Abuse, and Mental Health Administration, with supplemental grant 9035190 from the W.T. Grant foundation, New York, NY (Dr. Kessler, principal investigator).
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