In Zhu et al. [1], we present data showing that in California most Latino adult smokers (> 70%) are low-frequency smokers. Of these, about two-thirds are non-daily smokers, and the rest are low-rate daily smokers or chippers (consuming ≤ 5 cigarettes per day). We go on to call for explanations beyond withdrawal-based theories of smoking behavior. Based on the careful laboratory studies by Shiffman and colleagues [2,3], which demonstrate that chippers do not experience classic withdrawal symptoms, we suggest that, by extrapolation, non-daily smokers most probably do not experience such withdrawal symptoms either, because they regularly go without smoking for days.

DiFranza [4] contends that low-frequency smokers in fact do experience withdrawal symptoms and that Shiffman and colleagues' results cannot be generalized. He cites multiple studies, most dealing with adolescents who have not yet developed a daily smoking habit, showing that many of them show signs of dependence or report withdrawal symptoms. He suggests that the theory of sensitization–homeostasis provides a good explanation for the low-frequency smoking phenomenon as described in our study.

We share DiFranza's interest in finding new explanations for low-frequency smoking behavior among established smokers [4,5]. However, we doubt that looking for withdrawal symptoms among these smokers is likely to provide a satisfactory answer. We agree that many low-frequency smokers will report withdrawal symptoms, according to the definition of withdrawal and the methodology used to assess them in studies by DiFranza and colleagues [6,7]. Our failure to cite them is due mainly to what seems to us the ambiguity of the results reported and the inapplicability of their interpretations to our study. For example, as evidence of withdrawal, DiFranza [4] states: ‘We found that 43% of chippers felt a strong need to smoke when abstinent, and 40% had failed an attempt at cessation’. However, one would certainly expect low-frequency smokers to have urges to smoke (otherwise they would not have been smoking to begin with). In addition, although low-frequency smokers have high quit rates, it is certainly known that they do not succeed 100% of the time [8,9]. In other words, having urges to smoke or failing at quitting cannot be equated to experiencing withdrawal, even if there is overlap for some smokers. We appreciate the sensitization–homeostasis theory, but it is still within the withdrawal framework [10]. The applicability to our study results is not clear, as the theory does not generate predictions that low-frequency smoking will be the prevailing smoking behavior for any one particular group, in this case Latinos.

The final model needed to account for low-frequency smoking behavior will most probably require multiple variables on multiple levels. The aim of Zhu et al.'s paper [1] was not to take sides on the issue of whether individual low-frequency smokers ever experience something that should be classified as withdrawal symptoms. It was to suggest expanding the focus from looking for neuro-biological variables as the main explanation, to an examination of social–environmental variables, in order to account for a population phenomenon such as the one reported in Zhu et al.'s study. This is important not only for improving the explanatory power of theories of smoking behavior, but also for guiding tobacco control campaigns attempting to reduce smoking prevalence at the population level.


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  2. References
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