As expected, the success rate of females in the follicular phase (FFs) of the MC was significantly higher than that of females in the luteal phase (LFs). This difference was observed at the first data collection point, day 3, after all subjects were administered identical NRT medication but prior to the initiation of one of three levels of behavioral intervention. Thus, these results are independent of behavioral treatment intensity. The higher success rate in FFs in comparison to LFs and men persisted 1 week after treatment. In other words, the initial propensity of LFs to lapse/relapse was sustained even as they progressed through other stages of their cycle throughout treatment.
How could MC phase at the start of treatment influence women participant's behavior throughout? As stated, LFs either did not quit or relapsed early in treatment and failed to gain or regain abstinence over the course of treatment. It is conceivable that the combined discomfort of premenstrual and withdrawal symptoms at the time of quitting conferred a dual vulnerability, making initial abstinence more difficult and causing greater negative emotional reactions to their inability to abstain. Thus, LFs' initial lapse early in treatment was perpetuated. The results presented here emphasize the potential importance of MC phase at initial quit attempt in guiding treatment outcome.
A second possibility for the high and early relapse rate in LFs may reflect differences between the groups in cue responsivity. In an earlier reoprt, FFs had less craving to smoking stimuli than LFs, whereas male cue reactivity was not different from that of LFs.9
As these are the first studies to examine MC phase effects on smoking behavior that included a male control group, additional studies are necessary to determine if the effect is related to cue reactivity itself or to the effect of MC phase on cue reactivity.
As this is a retrospective study, it has its limitations. In this study, women were not stratified by MC phase at quit date, which could cause a selection bias. Although a possible caveat, the decision to quit may have been made when women were in a different phase from the one occurring at the quit date, as the screening process leading up to quit date varied from 2 days to 2 weeks across women. Regardless, the possibility of selection bias encourages future study wherein women are stratified according to MC phase. Another limitation to this study is the small sample size. Half the women participating in the original NRT study did not meet criteria to study MC phase, as many were close to menopause, using birth control methods, or had irregular menses. Future larger studies are necessary before firm conclusions on the role of MC phase in smoking cessation can be drawn. A third possible limitation is the slightly higher dependence scores and years smoking in the LFs compared with the FFs. However, as there were no significant differences in years smoking, cigarettes per day, or dependence (as measured by the FTND) between the groups, it is unlikely that these differences affected the results of this study.
MC phase was determined from the subject's self-report of the first day of the last menses. Physiological measurements of phase determination, considered by some as the paradigmatic tests of reliability, were not obtained in the original study. However, the only published study directly comparing several physiological measures with self-report found that none of them, including the gold standard of phase determination, anatomical definition by transvaginal ultrasound, were superior to self-report: “In all subjects, ultrasound confirmed expected cycle phase as predicted by self-report. …”12
These findings should be taken in the context of the significant health problem of smoking and its effects on women. The reality is that the number of adolescent and adult females who smoke is increasing. Women smokers face increased smoking-related deleterious health consequences compared with men, including increased risk of lung cancer. These factors emphasize the importance of identifying relapse predictors and revealing their underlying mechanisms. Understanding the role of MC phase in psychological and physiological nicotine withdrawal will aid in the development of effective smoking cessation strategies. The preliminary findings reported here warrant the attention of researchers and clinicians alike. Researchers may consider collecting and analyzing prospective data on premenstrual severity and self-reported and physiological determinants of phase. Clinicians may consider arranging quit dates to coincide with the follicular phase, as this approach is without risk and may increase women's chances of successfully quitting smoking.