Women find it more difficult to stop smoking during the follicular phase of the menstrual cycle, a study has found.

A randomised intent-to-treat trial involving 202 women between the ages of 18 and 40 who smoked at least ten cigarettes per day was carried out. The trial was specifically designed to assess how smoking relapse rates were influenced by the menstrual phase the quit attempt was started in.

Participants were motivated to stop smoking, and those receiving hormone treatment, obtaining nicotine from other sources or were pregnant or breast feeding were excluded. Participating women were randomised to stop smoking in either the follicular phase (cycle day 4-6 - the 'F' quit group) or luteal phase (6-8 days after the LH surge as monitored by home urine testing kits - the 'L' quit group) of the menstrual cycle. Participants were followed up for 26 weeks after their quit date.

Data on abstinence and relapse were collected by a variety of means, including self-completed diaries and biochemical measurements of breath CO. Withdrawal and craving were monitored by use of the Minnesota Nicotine Withdrawal Scale.

The study found that women in the 'F' quit group had significantly worse smoking cessation outcomes than women in the 'L' quit group, with fewer mean days to relapse. After

30 days, 86% of the F group had relapsed, compared with 66% of the L group (P=0.001).

Overall, 23% of the L group never relapsed, compared with 9% of the F group. There were no phase-related differences in withdrawal symptomatology

There is some evidence, as yet unexplained, that women find it harder to stop smoking than men and are more likely to relapse. Therefore, any findings which can improve quit rates for women are potentially valuable.

More research may be needed, but this study adds to existing evidence that ovarian hormones may have a role in nicotine addiction and quitting. In the future, primary care teams may find themselves setting quit dates for women smokers that tie in to a specific part of their menstrual cycle.

Allen SS, Bade T, Center B et al. Menstrual phase effects on smoking relapse. Addiction 2008;103:809-21