This study evaluates whether completing a short screening questionnaire about health behaviours in the waiting room before a primary care consultation decreases excessive substance use in young people aged 14 to 24 years. Young people consulting a primary care physician will randomly receive either a questionnaire about substance use or a questionnaire about physical activity. They will be contacted again 3, 6 and 12 months later and asked to complete a questionnaire about substance use. The proportion of young people with excessive substance use in each group will be compared. The researchers hypothesise that at three months this proportion will be lower in the group of young people having completed the initial questionnaire about substance use when compared to the group having completed the questionnaire about physical activity.

Background: Excessive alcohol and other substance use often begin in adolescence and contribute extensively to the development of non-communicable diseases and lifelong morbidity/mortality. In Switzerland, the prevalence of binge drinking (the most common mode of alcohol excess in adolescence) and other excessive substance use in young people is high, both in the general and in the primary care population. Since most young people visit a primary care physician at least once in any year, primary care offers an ideal context to individualize the preventive messages delivered in the community to favor behavior change.

Primary care physicians are encouraged to screen and provide brief interventions addressing excessive alcohol and other substance use in young people, but a range of barriers such as time constraints and insufficient training limit the implementation of these recommendations. Finding new ways of building on the potential of primary care whilst addressing these barriers is essential.

Several recent trials of brief primary care interventions showed substantial reductions (20% to 30%) in the proportion of participants who were excessive substance users at follow-up but no statistically significant differences between the intervention and control groups. Key authors have hypothesized that this could be due to assessment reactivity, i.e. when pre-intervention assessment itself encourages behavior change and thus serves as an intervention. Indeed, screening in the clinical context could act as an intervention and be as effective as a brief intervention within the consultation. To date this hypothesis has not been explored for young people attending primary care.

Methods: One of our previous trials (PRISM-Ado), and a pilot trial published in 2019, inform the methods of this parallel-group randomized controlled trial in primary care. Advisory panels of primary care physicians and young people contributed to the development of this protocol. Recruitment will take place in primary care practices in the French-speaking part of Switzerland. Young people between the ages of 14 and 24 years consulting for any health problem will be eligible. Up to 840 young people (approx 20 per practice) will be included and randomized to complete two different types of confidential pre-consultation screening surveys: one focusing on the assessment of binge drinking and other substance use (intervention group) and the other on physical activity (control group). Both surveys will include identical additional socio-demographic and health-related questions. The primary care physicians will not automatically have access to the answers provided in the surveys and participants will be free to decide if they wish to disclose them to their physician during the consultation. Follow-up phone interviews will take place at 3, 6 and 12 months. They will be identical for all participants and include all questions from the intervention and control questionnaires. The main outcome at 3 months follow-up will be the proportion of patients reporting binge drinking (≥1 episode) in the past 30 days. Secondary outcomes will include the proportion of young people reporting smoking (≥ 1 cigarette a day), electronic cigarette use (≥ once a day) and/or excessive cannabis use (≥1 joint/week) in the past 30 days. Analysis will be by intention to treat and will take into account clustering of participants within practices.

Expected value of the proposed trial: If our intervention proves effective, it will offer a simple, widely expandable method to encourage behavior change in young people consulting in primary care, thus contributing to a much-needed reduction in the burden of non-communicable diseases in the future. In addition, by providing a quantification of the effect of assessment reactivity per se, our study will provide key information for the design of future trials of interventions addressing substance use in young people attending primary care.

Inclusion Criteria:

- Patients aged 14 to 24 years consulting at the participating primary care practice for any motive.

Exclusion Criteria:

• Acute illness requiring immediate attention of the physician
• Severe mental health conditions requiring treatment in a specialized setting
• Young person not consulting as a patient at the practice (e.g. accompanying friend or partner)
• Inability to read the trial information in French or to provide independent consent.

Participants: Although they cannot be masked to the content of the intervention (questionnaire), they are only informed that the study is about health behaviours in general and not specifically about substance use. Thus, they are masked as to whether they are in the intervention or control group.