Nakajima M, et al. - In view of the observation that menstrual cycle phase plays a role in smoking withdrawal symptoms and craving, and stress increases these symptoms, researchers assessed if the stress regulatory mechanism is associated with menstrual phase and withdrawal symptoms. Findings demonstrated the influences of the menstrual cycle phase on stress response among smokers. This was observed to be exhibited by a reduced cortisol response to stress in the luteal group relative to the follicular group among smokers. Nonsmokers did not exhibit this menstrual phase difference.