The purpose of this study is to determine whether a mobile-phone based intervention is effective in supporting smoking cessation among Chilean women

This protocol corresponds to a single-blind, two-arm, randomized clinical trial of a smoking cessation intervention based on a mobile-phone app. Eligible participants are Chilean women from the Metropolitan Region, who smoke daily (at least one cigarette per day) or weekly (at least 7 cigarettes per week), and who are willing to make a quit attempt within one month of enrollment. Study will be advertised on the local radio, primary care centers, smoking cessation services and through social media campaigns. Study information will be available online. Potential participants will be asked to register their interest by sending an email to the study. Research assistants then will contact respondents by phone in order to complete a baseline questionnaire about sociodemographic variables, characteristics of tobacco consumption, and to assess eligibility for the study. Eligible participants will be then randomized to the intervention group or control group using a computerized and automated process, in blocks of 6. A minimization algorithm balancing for Fagerstrom score for nicotine addiction (≤5, >5) will be used. Researchers who will gather data and those who will measure carbon monoxide in exhaled air will be masked to treatment allocation.

Each participant will be emailed the link with either the intervention or the control version of the mobile-phone app. Once participants download the app, they will be asked to provide informed consent by clicking the "accept" or "reject" button in the app.

Participants randomized to the intervention app will be sent motivational and preparatory content for the first two weeks, and they will be asked to set a quit date within 4 weeks from enrollment. The mobile app will send an average of 4 messages per day during the first month after quit date, followed by three messages per week up to the end of the study at month 6.

The intervention program was designed based on current best evidence on strategies to support smoking cessation, and included work of Chilean experts in smoking cessation. The design of the intervention app also included the opinion and preferences of potential participants who participated in focus groups during intervention design. The intervention app includes motivational messages, tips on stress management, on how to ask support from friends and family, how to use distraction techniques and how to deal with cravings, lapses and early relapse.

The intervention app also includes a "help button" which provides extra messages in case of cravings and a "lapse/relapse button", which provides advice about what to do if the participant returned to smoke. The control group will receive a control app which will send 1 message every two weeks thanking participants for taking part in the study, and encouraging them to stay in the study for the 6 month follow-up period. After completing the 6-month follow-up evaluation, the control group will be offered access to the intervention app.

Women will not receive financial compensation for their participation in the study. In order to increase retention, participants in both arms will be told that they would be entered into a lottery for different prizes after answering the 6-month follow-up questionnaire.

For the 4-week, 3-month and 6-month follow-up, a link to an electronic follow-up questionnaire will be emailed to all participants. Reminders will be sent to non responders and if they still do not respond, additional email reminders will be sent. If participants still do not respond, research assistants will call them by phone in order to capture the primary outcome of the study. At 6-month follow-up, participants who reported having quit smoking will be asked to attend to the local primary care center in order to measure carbon monoxide in exhaled air. All measurements will be performed by research assistants who are masked to treatment allocation.

Sample size was calculated based on previous studies. Twenty-eight percent quitting in the intervention group and 13% in the control group was expected. To achieve 90% power with a significance level of P ≤ .05 (2-sided), and including a 20% attrition for the 6 month follow-up evaluation, a sample size of 400 was estimated. In order to take into account that the size effect associated to the intervention could be lesser in Chile than the reported for other countries, investigators defined a 90% power for the sample size calculation.

Investigators plan to conduct analyses for the whole sample and also for subgroups of age (<35 years, ≥35 years), nicotine addiction (Fagerstrom score ≤5, >5), educational level (<8 years, 8-12 years, ≥12 years), and use of other smoking cessation treatments or services during the trial (yes, no).

All statistical analyses for clinical effectiveness will be undertaken on an intention-to-treat basis. For missing observations in the primary outcome, two methods will be used: last value carried forward method and multiple imputation method, as attempts to correct for potential bias caused by missing data.

Analyses for adverse effects outcomes will be performed on a per-protocol basis.

Inclusion Criteria:

• Smoker of at least 1 cigarette per day or at least 7 cigarettes per week in the last 6 months
• Willing to make a quit attempt in the next month
• Owns and uses an Android cell phone
• Lives in the Metropolitan Region and has no plans to move in the next year

Exclusion Criteria:

• Severe mental disability or inability to read or answer a telephone survey
• Screening positive for hazardous drinking behavior or active alcohol use disorder

Eligible participants will be randomized to the intervention group or control group using a computerized and automated process. An email will be automatically sent to the participants with the link to download the corresponding version of the mobile-phone app (intervention app or control app). Researchers who will gather data and those who will measure carbon monoxide in exhaled air will be masked to treatment allocation.