The traditional theoretical model describing the onset of nicotine dependence holds that the sensory and social rewards derived from smoking are the sole motivators of adolescent tobacco use for the first several years.18,19
According to this model, escalation in tobacco use results from tolerance to the pleasure of smoking, and smokers develop dependence when their pursuit of pleasure causes them to smoke at frequent intervals throughout the day.
The sensitization-homeostasis theory contradicts the traditional model.20
It proposes that symptoms of dependence that appear during nondaily smoking motivate continued tobacco use. According to this model, even smoking at monthly intervals entails a strong risk for developing dependence. Supporting this theory are 4 independent studies showing that symptoms of dependence develop during nondaily smoking, sometimes quite soon after the first cigarette.6–8,10
The findings of the current study, demonstrating that monthly smoking may increase the risk of developing dependence nearly 10-fold, support the sensitization-homeostasis theory.
The sensitization-homeostasis theory also posits that, once symptoms of craving and withdrawal appear, smokers experience symptoms whenever they go too long without smoking.20
At first, smoking intervals may be comfortably spaced at intervals of days or weeks; as repeated exposures promote tolerance, smokers must smoke at more-frequent intervals to keep symptoms at bay. The theory asserts that early symptoms drive an escalation in the frequency of smoking to daily use. In this study, the early appearance of dependence symptoms increased the risk of progression to daily smoking (HR: 6.8), and the number of symptoms predicted the magnitude of escalation in smoking frequency that occurred between interviews.
Previous studies found that dependence severity correlated with current smoking frequency and cumulative lifetime exposure,21–25
but we think that our study is the first to demonstrate that increased frequency of smoking puts youths at risk for more-rapid development and progression of dependence. This is important, because it suggests a dose-response effect of early nicotine exposure on the development of dependence.
Our findings suggest that the loss of autonomy over tobacco use proceeds in a typical sequence, with some individual variation. The order in which symptoms typically present is consistent with the mechanism described for the development of dependence under the sensitization-homeostasis theory. Among the symptoms assessed in this study, a strong urge to smoke was typically the first to appear, followed by withdrawal symptoms. These symptoms typically develop before the onset of daily smoking. In previous studies, the early appearance of dependence symptoms was very strongly predictive of future smoking5,8
and withdrawal symptoms predicted relapse among adolescent smokers, which indicated their clinical importance.21,26
Difficulty controlling use may not be reported until later in the course of symptom development, because refraining from smoking where it is not allowed may not be a problem when dependence can be satisfied by smoking less often than once per day.
The most important observation from our study is that the early course of nicotine dependence seems to involve a vicious cycle in which exposure to nicotine through smoking promotes the early development of craving and withdrawal, these symptoms drive an escalation in smoking frequency as tolerance develops, and this escalation promotes the development of additional symptoms of dependence. The strength of the reciprocal relationship between diminished autonomy and smoking frequency decreased over time. There are several potential explanations for this. A previous study found that the correlation between smoking frequency and levels of the nicotine metabolite cotinine decreased rapidly as consumption exceeded 4 or 5 cigarettes per day.27
Therefore, at a certain level of cigarette consumption, the dose of nicotine received may reach a physiological steady state with nicotine requirement within individual persons. This suggests that the urge for escalating tobacco use diminishes once the dose of nicotine is sufficient to satisfy physiologic needs or to saturate receptor sites. Alternatively, at higher levels of consumption, differences in smoking frequency may reflect only individual differences in levels of tolerance to nicotine that may be unrelated to dependence.28
In our study, some youths began smoking daily from their first cigarette, although they had no symptoms that would require them to do so. A possible explanation for frequent smoking in the absence of symptoms is easy access to tobacco.29,30
Reducing the accessibility of cigarettes might slow the progression of dependence.
Our subjects typically did not report feeling addicted at the time when they experienced craving and withdrawal. Apparently, youths do not recognize strong craving and withdrawal as symptoms of addiction. Educating youths to recognize early symptoms of dependence may be a useful goal for secondary prevention programs, because it might prompt earlier and more successful cessation efforts.
Our findings are consistent with a study by Gervais et al,7
which found that craving typically precedes withdrawal and both symptoms typically precede daily smoking. However, our study found that feeling addicted was a late symptom, in contrast to the findings of Gervais et al,7
who reported that self-diagnosed mental addiction typically preceded all other symptoms. This discordance may be attributable to differences in how these terms are interpreted by smokers.
Strengths of this study include the close, long-term, follow-up monitoring of novice smokers, with prospective data collection on symptom development and detailed records of smoking frequency, including dates for each event. The smoking prevalence in our cohort was comparable to that for the state of Massachusetts.31
A recent study demonstrated that youths’ reports of symptoms of diminished autonomy are valid and is not merely the result of false reporting or expectations based on the observations of other smokers.32
Study limitations include the limited number of subjects who had all 4 symptom types and the use of a geographically limited convenience sample. The results may not be applicable to individuals who initiate smoking after adolescence. The earliest dependence symptom that was assessed in this study was strong craving. However, a recent case series indicated that strong craving is not the initial symptom of dependence, because it may be preceded by recurrent wanting, which is milder and less intrusive than craving.32
In this study, youths were not asked about wanting and were not trained to recognize symptoms of dependence. If youths were taught to recognize symptoms or were given the opportunity to describe them in their own terms, they might report symptoms earlier. Between-subject variations in awareness and recognition of symptoms could contribute to variations in the order of symptom reporting.