Rationale: Compensation or compensatory smoking, accurately defined, deals with the question of whether switching to cigarette brands with different smoke yields is associated with a change in smoke uptake proportional to the change in machine-derived yields. The issue of compensation is important because it bears on whether switching to "lighter" brands means lower overall smoke intake or not.
Objectives: The present review investigated whether and to what extend low yield cigarettes are smoked more intensively. In addition, published data on whether nicotine, "tar", or any other smoke constituent or property influence compensational smoking are summarized.
Methods: The studies on compensation were classified as follows: (1) studies on smoking behaviour in relation to cigarette yields (with and without brand switching); (2) studies on compensation for nicotine (switching between cigarettes which differ "only" in their nicotine yield, nicotine supplementation, manipulation of renal nicotine excretion, administration of nicotine agonists or antagonists); (3) studies on compensation for other factors (influence of tar, taste, irritation, draw resistance). In order to quantify the degree of compensation, an index is defined and applied to selected brand switching studies. This compensation index determines, in relative units, the degree to which a smoker responds to a change in smoke yields with a change in smoke uptake measured by suitable biomarkers. The role of vent blocking is also briefly discussed.
Results: Most of the studies which compare the smoking behaviour when smoking cigarettes with different smoke yields supply evidence for "partial" compensation, suggesting that cigarettes with lower yields are smoked more intensively than those with higher yields. These studies also show that a change in the daily number of cigarettes is not a common mechanism of compensation. Effective vent blocking during smoking is a rare event and can therefore also be regarded as an uncommon mechanism of compensation. Evaluation of a suitable subset of brand-switching studies revealed an average compensation of 50-60% of the nicotine yield. Compensation tended to be more complete when changing to cigarettes with higher yields than when changing to cigarettes with lower yields. In general, brand-switching studies do not supply information on the underlying causal factors responsible for compensatory smoking. Results of the nicotine supplementation studies are not conclusive: some report evidence of nicotine titration, others do not. A general problem with this type of investigation is that continuous nicotine application does not mimic the spike-wise application with cigarette smoking, and may lead to nicotine tolerance. There is limited evidence that cigarettes were smoked more intensively when the urinary clearance of nicotine was increased. A small number of studies provide some evidence that smoking intensity increased after smokers were administered a nicotine antagonist. Several reports indicate that tar, taste and sensory properties of the smoke as well as the draw resistance of the cigarette may play a role in compensatory smoking. Low-yield cigarettes usually have reduced pressure drops which smoke researchers have suggested leads to increased puff volume. This effect seems to be independent of the smoke yield of the cigarette. There is also some evidence that some smokers maintain a consistent pattern of smoking which works independent of any changes in nicotine or tar yields, taste or design features of the cigarette ("functional autonomy").
Conclusions: The available data suggest that smokers partially compensate for a different smoke yield. While the factors and their interaction responsible for compensational smoking are not fully understood, there are data suggesting that a subgroup of smokers may partially compensate for nicotine. Even in this subgroup of smokers, however, the relative importance of the pharmacological versus