Background: It has been suggested that anti-smoking therapy gives encouraging results, but this has not been verified by well-randomized study protocols. The present study was a randomized controlled trial of varenicline vs nicotine patch in adult smokers for comparison of efficacy, safety and withdrawal symptoms. Methods and Results: The 32 adult smokers were randomly divided into a varenicline group (VG, n=16) and a nicotine patch group (NG, n=16). The primary endpoints were the 12- and 24-week smoking-abstinence rates, safety and withdrawal symptoms including stress. No significant difference in abstinence rates was observed between the 2 groups over weeks 9-12 (71.4% vs 78.6% in the VG and NG, respectively), and weeks 9-24 (64.3% vs 71.4%, respectively). The frequencies of inability to concentrate at 2, 4, and 8 weeks, and wakeful nights at 2 weeks were higher in the VG than in the NG. Adverse side-effects associated with a gastrointestinal disorder occurred in 14 cases and 1 case in the VG and NG, respectively, and skin allergy was seen in 0 and 9 cases, respectively. Conclusions: The selection of treatment depends on the balance of desired acuteness of cessation of smoking and side-effects, such as psychiatric and gastrointestinal problems or skin allergy. (Circ J 2010; 74: 771-778)