ed a standardised measure of mental health. 12 13 No previous literature has discussed the possible impact of smoking reduction on mental health and how this may differ from abrupt cessation; however, based on what is currently known about tobacco and mental health, there are three possibilities. As the chemical components in tobacco have a short half-life, psychological withdrawal symptoms occur shortly after smoking a cigarette, and these symptoms become more severe with longer periods of abstinence. 14 15 Thus, the first possibility is that by reducing cigarette consumption and, in turn, increasing the duration between cigarettes, the smoker may experience longer periods of and more intense withdrawal symptoms such as irritability, depressed mood and anxiety, thus leading to worsened mental health. Mental health may also worsen for some smokers on reduction if they derive a mental health benefit from smoking, according to the self-medication hypothesis. 16 Second, there is evidence that higher levels of tobacco consumption are associated with poorer mental health, 17 18 and that stopping smoking is associated with improved mental health. 11 Therefore, it follows that if there is a dose–response association between tobacco consumption and mental health, reducing tobacco consumption may be associated with improvements in mental health. The third hypothesis is that mental health could remain unchanged. After maintaining reduced cigarette consumption, the smoker may adapt to their new tobacco consumption level and their mental health will remain the same. Another reason it may not change is that the association between poor mental health and smoking could be caused by a common factor 19 which would not be expected to change on smoking reduction. If smoking reduction worsens mental health, this may not be the most appropriate route to quit for those with mental health disorders or who are experiencing stress. However, if smoking reduction improves mental health or lea Results After adjustment for confounding variables, the differences for reducers compared with continuing smokers were: regression modelling −0.6 (95% CI −4.4 to 3.2) and propensity score matching 1.1 (95% CI −2.0 to 4.1). Conclusions Smoking reduction, sustained for at least 12 weeks, was not associated with change in mental health, suggesting that reducing smoking was no better or worse for mental health than continuing 3 A significant proportion of smokers in countries with mature tobacco epidemics report mental health problems. 4 Moreover, smokers with and without mental health problems report that smoking offers mental health benefits. 5–10 Therefore, the effect of smoking reduction on mental health is a particular concern. There is strong evidence that stopping smoking is associated with improved mental health, and this improvement may result from breaking the tobacco withdrawal cycle. 11 However, it is not clear whether reducing daily cigarette consumption is associated with change in mental health. As the chemical components in tobacco have a short half-life, psychological withdrawal symptoms occur shortly after smoking a cigarette, and these symptoms become more severe with longer periods of abstinence. 14 15 Thus, the first possibility is that by reducing cigarette consumption and, in turn, increasing the duration between cigarettes, the smoker may experience longer periods of and more intense withdrawal symptoms such as irritability, depressed mood and anxiety, thus leading to worsened mental health. Mental health may also worsen for some smokers on reduction if they derive a mental health benefit from smoking, according to the self-medication hypothesis. Effect estimates from PSM provide evidence that an association is not due to membership bias or observed confounding, and therefore offer stronger evidence of a causal association. 20 21 We compared results from these approaches to determine if there was evidence of an association between smoking reduction and change in mental health. Method This study followed STROBE reporting guidelines for observational studies. 22 PSM procedures were conducted and reported following criteria outlined by a review of PSM methodology. As with many observational analyses, our initial approach using regression was at risk of bias through confounding and group membership. The propensity score approach can overcome bias through group membership and offers more control for confounding, 20 21 but gave a similar result to the regression modelling in this case. However, the estimates from PSM were a little more imprecise by reducing the effective sample size. Implications Many smokers and clinicians are reluctant to address patients’ smoking behaviour for fear that they may cause harm to mental health. 40 41 This study adds to the evidence from previous studies that reducing daily cigarette consumption was not associated with change in mental health. 12 13 Therefore, on average, clinicians can be confident that smoking reduction is unlikely to negatively influence patients’ mental health. Conclusion If smoking reduction was found to be associated with worsened mental health, this could be due to increasing the duration of withdrawal symptoms, 42–45 thus supporting the hypothesis that repeated exposure to tobacco can worsen mental health through the withdrawal cycle. 43–45 Equally, this could indicate that by reducing the frequency of any psychological benefit of tobacco the smoker experiences worse mental health. 16 However, based on these data analysed in two ways, the evidence here was consistent with previous studies and show no association between smoking reduction and change in mental health, thus suggesting that on average smoking reduction is not any better or worse for mental health than continuing to smoke. Clinicians offering smoking reduction as a route to quit can be confident that on average smoking reduction is not associated with negative change in mental health.