Behavioural studies in humans: anxiety, stress and smoking

Numerous observers have reported that smokers smoke more under stressful conditions. The most frequent explanation is that nicotine reduces anxiety, an intervening variable identified as a negative reinforcer for smoking behaviour. The conditions under which anxiety reduction occurs in response to smoking, however, have not been well defined, nor are underlying mechanisms well understood. There are several possible explanations, including Schachter's theory based on stress-induced changes in urinary pH and the hypothesis of endogenous opioid involvement. The work of Collins and his associates in animals has shown that genetic variations in corticosteroid responsiveness to nicotine are associated with differences in sensitivity to nicotine. Research in our laboratory has extended to humans Collins' findings that sensitivity to nicotine is inversely related to corticosteroid activity. We also found that the combination of a psychological stressor and smoking produced additive effects on cortisol release in humans. These findings suggest a novel way of explaining the interaction between smoking and stress, in that increased nicotine intake in the context of stress may in part reflect behavioural compensation for diminished sensitivity to nicotine when corticosteroid activity is enhanced by the stressor.