There are some limitations. Firstly, in this analysis we used study level data instead of individual level data so we were unable to determine whether differences in the adverse events were because of greater quit rates in the varenicline group relative to placebo. Secondly, because of the small number of suicides and attempted suicide reported (n=6), we cannot rule out major beneficial or adverse effects of varenicline for this outcome (Peto odds ratio 1.67, 95% confidence interval 0.33 to 8.57). Thirdly, there was potential for heterogeneity in the reporting of adverse events. Authors used a range of methods to record adverse events including self report, open ended questions, structured questionnaires, side effect checklists, and case reports coded to the Medical Dictionary for Regulatory Activities (MedDRA, www.meddra.org). All of the industry sponsored trials coded adverse events using MedDRA. Fourthly, we excluded two studies69 73 from the review as the maximum dose of varenicline used in these studies was only 1 mg once a day—that is, half of the recommended maximum dose. Hong and colleagues examined varenicline treatment in 20 smokers and
