The primary purpose of the current study is to compare the effect of SMS-textmessage vs e-mail reminders on user engagement and proportion of reported quit attempts in an online smoking cessation intervention.

Web- and mobile phone health behavior change interventions, including smoking cessation programs, offer great promise, but little is known about how such interventions should be designed to increase user engagement. The primary purpose of the current study is to compare the effect of SMS-textmessage vs e-mail reminders on user engagement and proportion of reported quit attempts in an online smoking cessation intervention.

The investigators propose a 2-arm RCT with 700 adult study participants that all receive a best practices web-based smoking cessation program designed for use on smart phones (web-app). The intervention includes a ten day preparation phase, in which participants continue smoking. On the eleventh day (and onward) the user will receive a session in which (s)he is asked whether (s)he has quit smoking or not. If not, the user will receive additional treatment sessions until (s)he reports having quit (or dropped out of the study). Each day (for up to 14 days) a new unique session is assigned to the user. However, if the user does not log on to the web-intervention and starts using the session by noon on the second day after assignment, the user will receive a reminder to do so. When a user is to be sent a reminder for the first time, (s)he will be randomized to either receive such reminders by SMS or by e-mail.

The primary outcome is reporting a quit attempt or not. Secondary outcomes include number web-sessions started and completed and time spent navigating sessions after the first reminder is received.

Inclusion Criteria:

• 18 years or older
• current smoker
• determined to or considering to quit smoking
• provide valid e-mail address
• provide valid norwegian cell phone number
• complete a baseline questionnaire
• start using the intervention (pushing the next page button one time or more on the first session provided)
• has not logged on to any of the online session within noon on the second day after that particular session was made available

Exclusion Criteria:

• Not starting the first treatment session
• Taking every treatment session on time (no need for reminders, and thus not randomized)

The recruitment procedure and the treatment is fully automated and delivered by web, e-mail and SMS-textmessages - i.e., the participant is not contacted by any care providers, investigators or assessors during recruitment or treatment.