This 6-week, randomized, open-label pilot study estimated the treatment effect size of gabapentin (n = 17) compared with bupropion SR (n = 19) for smoking cessation, thereby allowing sample size calculations for a definitive comparison study. The primary outcome measure was smoking cessation. Secondary outcome measures included smoking reduction and withdrawal severity. Gabapentin was less efficacious than bupropion for smoking cessation but was associated with fewer dropouts from adverse effects. Withdrawal severity was less with bupropion. Bupropion remains the first-line non-nicotine pharmacotherapy for smoking cessation. Further study is required to determine if gabapentin has any useful role in smoking cessation. Based on our primary outcome measure, 79 subjects would be required in each treatment group of a two-armed study to achieve 90% power for detecting a difference in efficacy between gabapentin and bupropion.