Table 1 and appendix 2 describe study characteristics. The trials included 11 146 participants (6015 patients were randomised to receive a maximum of varenicline 1 mg twice daily and 5131 patients received a placebo). Of these randomised patients, 10 998 were evaluable for adverse events (5931 in the varenicline group and 5067 in the placebo group). The duration of treatment ranged from one week to 52 weeks, while study duration ranged from eight days to 53 weeks. Eighteen trials (61.3% of all participants) included cigarette smokers from the general population with no history of psychiatric illnesses (table 2). In trials that included cigarette smokers (39 trials) participants smoked an average of 20 cigarettes a day for 26.6 years in the varenicline group and 20 cigarettes a day for 26.2 years in the placebo group. Loss to follow-up ranged from 0% to 60% in both groups (appendix 2). In 12 trials losses to follow-up were higher in the varenicline group than the placebo group, whereas in 17 trials losses to follow-up were higher in the placebo group than the varenicline group.
