Do early experiences with cannabis vary in cigarette smokers?

Washington University School of Medicine, Department of Psychiatry, 660 S. Euclid, CB 8134, Saint Louis, MO 63110, USA. Electronic address: .
Drug and alcohol dependence (Impact Factor: 3.42). 09/2012; 128(3). DOI: 10.1016/j.drugalcdep.2012.09.002
Source: PubMed


We examine whether regular cigarette smokers were more likely to be exposed to and use cannabis at an earlier age, and further, upon initiation, whether their initial experiences with cannabis varied from those reported by never/non-regular cigarette smokers.

A sample of 3797 Australian twins and siblings aged 21-46 years was used. Survival analyses examined whether cigarette smokers were at increased likelihood of early opportunity to use cannabis and early onset of cannabis use. Logistic regression examined whether cigarette smokers reported greater enjoyment of their cannabis experience, inhaling on the first try, differing positive and negative initial subjective reactions, smoked cigarettes with cannabis the first time and were more likely to try cannabis again within a week.

Regular cigarette smokers were more likely to report an earlier opportunity to use cannabis and early onset of cannabis use. Regular cigarette smokers were also considerably more likely to have enjoyed their first experience with cannabis and reported higher rates of positive initial reactions. They were more likely to report inhaling on the first try and smoking cigarettes with cannabis. Potentially negative subjective reactions were also elevated in regular cigarette smokers. Importantly, cigarette smokers were at 1.87 increased odds of smoking cannabis within a week of their initial use.

These findings indicate that the well-known overlap in cannabis and cigarette smoking behaviors may evolve as early as opportunity to use and extend through the course of the substance use trajectory.

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    ABSTRACT: Initial subjective reactions to cannabis and tobacco, broadly classified as positive or negative, have previously been explored for their associations with onset and maintenance of subsequent abuse/dependence. We examine (a) the factorial architecture of self-reported initial reactions to cannabis and tobacco; (b) whether these factors associate with concurrently reported age at onset of DSM-IV diagnosis of nicotine dependence and cannabis abuse/dependence; and (c) estimate heritable variation in and covariation between the factors. Factorial and exploratory structural equation modeling was conducted to examine the factor structure of initial reactions. Cox proportional hazards modeling was employed to examine their association with time to onset of diagnosis of DSM-IV nicotine dependence and cannabis abuse/dependence. Classical twin modeling, using univariate and multivariate models, was used to parse variance in each factor (and the covariance between factors) to their additive genetic, shared environmental and non-shared environmental sources. General population sample of Caucasian female twins aged 18-32 years, with a lifetime history of tobacco [N=2393] and cannabis [N=1445] use. Self-report of initial subjective reactions to tobacco (cigarettes) and cannabis the first time they were used and time to onset of lifetime history of DSM-IV diagnosis of abuse (cannabis) and dependence (cannabis or nicotine). Factors representing putatively positive and negative reactions to cannabis and tobacco emerged. Initial reactions to tobacco were associated with onset of DSM-IV diagnosis of nicotine dependence and cannabis abuse/dependence while initial reactions to cannabis were associated with onset of DSM-IV diagnosis of cannabis abuse/dependence alone. Genetic factors played a moderate role in each factor (heritability of 27-35%, p < 0.05) with the remaining variance attributed to individual-specific environment. Covariation across the factors indexing positive and negative initial reactions was attributable to genetic sources (rg=0.09-0.55, p < 0.05), and in some instances, to overlapping individual-specific environmental factors (re=0.17-0.28, p < 0.05). Initial subjective reactions to tobacco are associated with later onset of DSM-IV diagnosis of nicotine dependence and cannabis abuse/dependence while initial subjective reactions to cannabis are only associated with onset of diagnosis of DSM-IV cannabis abuse/dependence. Genetic factors underpin the overlap across the factors representing initial reactions, both positive and negative.
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