Nesbitt's Paradox resolved? Stress and arousal modulation during cigarette smoking.

Nesbitt's Paradox states that cigarette smoking generates physiological and psychological changes which are normally incompatible, namely increased arousal together with decreased stress. This review confirms these changes, but shows that they are dependent upon various factors, particularly the degree of nicotine deprivation. Thus the relaxant properties of smoking reflect the relief of irritability which develops between cigarettes. The deleterious mood effects of abstinence explain why smokers suffer more daily stress than non-smokers, and become less stressed when they quit smoking. Deprivation reversal also explains much of the arousal data, with deprived smokers being less vigilant and less alert than non-deprived smokers or non-smokers. Nicotine can, however, display genuine stimulant properties, although due to repeated abstinence effects the average arousal level of smokers is generally similar to non-smokers. Mood normalization also explains why nicotine is so addictive, with regular smokers needing nicotine just to "function" normally. Finally, Nesbitt's Paradox also assumes that arousal and emotionality are associated with each other. Yet factor analysis of mood and personality questionnaires shows that these two dimensions are statistically independent, with the stress and arousal changes during smoking also generally uncorrelated. Nesbitt's Paradox is therefore not actually a paradox; it never was a paradox.