Participants

The app respondents were recruited through the app. Because of an administrative problem (data on age was unfortunately missing), this study used data collected from March to October 2018 when the age question was added to the questionnaire. We did not intend to use exclusion criteria. However, we would inspect the data, for example, the open-ended comments in the questionnaire and cannabis use variables, to examine whether there were respondents who were not ‘real’ cannabis users (e.g., relatives, health workers) or who reported unrealistic data (e.g., reported cannabis use for >30 days in the last month). To make the comparison between groups reliable, we excluded those with Severity of Dependence Scale (SDS) <4 in analyses, similar to the inclusion criteria in the CCP (see below). The questionnaire included a question regarding how the respondent intended to use the app (app alone or combined with other face-to-face services).

The comparative sample was recruited in three municipally based CCP centers in Norway (Kristiansand, Oslo, and Fredrikstad) from January 2013 to December 2016. The target group was individuals who engaged in regular or daily cannabis use, and who were motivated to quit cannabis. Some participants came into contact with the centers through support services in the cities (healthcare services, social security and welfare services, child welfare services, and school healthcare services), but no formal ‘referral’ was required. Many obtained information through friends, other users, or the internet and made direct contact themselves. The main aim of the CCP was to quit cannabis smoking, and participants were advised to set a quit date during the first part of therapy. The formal inclusion criterion was SDS score ⩾4. Youths under age <16 years were excluded from the CCP study.