Participants
The target population of the main trial was Swedish adults seeking help online to reduce their alcohol consumption. Individuals were required to be at least 18 years of age, have access to a mobile phone, and be classified as having harmful alcohol use according to Swedish guidelines. At the time of data collection, this was defined as either drinking more than 9 (female) or 14 (male) standard drinks of alcohol per week (total weekly consumption) or drinking more than 4 (female) or 5 (male) standard drinks on a single occasion at least once a month (heavy episodic drinking). A standard drink is in Sweden defined as 12 g of alcohol. All study materials were in Swedish, and so individuals who did not comprehend Swedish well enough to understand these were implicitly excluded.Participants were recruited to the trial using web search engine advertisements (Google, Yahoo, Bing) and Facebook. Individuals interested in the study sent a text message to a dedicated phone number. Within 10 min, they received a text message with a hyperlink that took them to a Web page asking for informed consent. Those who consented were asked to respond to a baseline questionnaire (which also assessed eligibility). The questionnaire included questions on demographics, current alcohol consumption, and three single item measures of confidence in one’s ability to reduce drinking (confidence), perceived importance of reducing drinking (importance), and knowledge of how to reduce drinking (know-how). Eligible participants were randomised after responding to the baseline questionnaire to either receive the novel digital alcohol intervention or to a control group. Drinking behaviour (weekly consumption and episodes of heavy drinking) was measured at 2-month and 4-month follow-up. The control group were provided with information regarding the risks associated with alcohol consumption and informed that they would receive access to the support tool after four months (waiting list design). There were no other differences between the control and intervention groups apart from the control group being given access to the novel intervention following completion of the 4-month follow-up. The demographics of the full cohort and those who engaged with the prompts module (N = 476 respondents) within each group (intervention and control) are shown in Table 
Baseline characteristics of total participants in the intervention and control groups, and those who used the prompts module