Objective: To evaluate the effectiveness of an intervention to help people to quit smoking throughout an chat bot compared with usual assistance to increase long-term rates of nicotine abstinence in smoking outpatients with biochemical validation at 6 months. Design: Pragmatic, randomised, controled and multicentric clinical trial. Six months follow-up. Setting: Health Care centers of Madrid Health Service. Participants: Smoking outpatients eighteen years and older who came to Health Center and accept help to quit in the next month. N = 460 smokers (230 in each arm), who will be recluted before ramdomization. Interventions: Intervention group: Use of an evidence-based Chat bot for smoking cessation. Control group: Usual care (Madrid Health System Portfolio). Main Measure: Continuous tobacco abstinence at six months biochemically validated (carbone monoxide in exhalled air). Analysis: With intention-to-treat principle. Proportion difference of continuous abstinence at 6 months between groups with 95% confidence interval. Logistic regression model dependent variable.

Funding: Instituto de Salud Carlos III (Spanish Goverment), 2017 announcementof Health Investigation Projects (AES 2017),expedient number PI17/01942.