Quit rate (7-day point prevalence) for long-term nicotine replacement therapy users in the varenicline and placebo groups from weeks 2 to 52, verified by expired carbon monoxide (except week 36 which was a telephone visit). Quit rate (7-day point prevalence) for long-term nicotine replacement therapy users in the varenicline and placebo groups from weeks 2 to 52, verified by expired carbon monoxide (except week 36 which was a telephone visit). Modified from [23]. Philip Tønnesen Eur Respir Rev 2013;22:37-43 ©2013 by European Respiratory Society