Rationale: The view of smoking as an addiction to nicotine implies that nicotine is an addictive drug and a primary reinforcer. However, nicotine other than in tobacco does not appear to be very rewarding for smokers. This potential anomaly to the nicotine addiction thesis is resolved by the proposition that the reward associated with smoking depends on "high-nicotine boli." According to the nicotine delivery kinetics hypothesis, smoked nicotine reaches the brain in 5-10 s in high concentrations, which provide reinforcing "hits" of nicotine to the brain.
Objectives: Because of its essential role in the nicotine addiction thesis, this review set out to examine the current empirical basis of the nicotine delivery kinetics hypothesis.
Materials and methods: We reviewed studies that bear on two questions: First, does nicotine from cigarettes reach the brain significantly faster than from other nicotine delivery devices? Second, is there a relationship between delivery kinetics and any rewarding effects of nicotine?
Results: There is little empirical support for the nicotine delivery kinetics hypothesis. Several studies found that arterial nicotine levels associated with smoking are much lower than predicted by the nicotine delivery kinetics thesis and not higher than with other nicotine delivery devices. More importantly, comparisons of nicotine delivery devices with varying speeds of delivery do not suggest any correlation between nicotine delivery profile and subjective reward.
Conclusions: This review indicates that the wide endorsement of the nicotine delivery kinetics hypothesis is unjustified. Critical research is required to resolve the anomalies within the nicotine addiction theory of smoking.