Introduction: A digital programme, MoodHwb, was co-designed with young people experiencing or at high risk of depression, parents/carers, and professionals, to provide support for young people with their mood and wellbeing. A preliminary evaluation study provided support for the programme theory and found that MoodHwb was acceptable to use. The present study aims to refine the programme based on user feedback, and to assess the acceptability and feasibility of the updated version and study methods. Methods and analysis: Initially, this study will refine MoodHwb with the involvement of young people, including in a pre-trial acceptability phase. This will be followed by a multi-centre feasibility randomised controlled trial comparing MoodHwb plus usual care with a digital information pack plus usual care. Up to 120 young people aged 13-19 years with symptoms of depression and their parents/carers will be recruited through schools, primary mental health services, youth services, charities, and voluntary self-referral in Wales and Scotland. The primary outcomes are the feasibility and acceptability of the MoodHwb programme (including usage, design, and content) and of trial methods (including recruitment and retention rates), assessed two months post-randomisation. Secondary outcomes include potential impact on domains including depression knowledge and stigma, help-seeking, wellbeing and depression and anxiety symptoms measured at two months post-randomisation. Ethics and dissemination: The pre-trial acceptability phase was approved by the Cardiff University School of Medicine Research Ethics Committee (REC) and the University of Glasgow College of Medicine, Veterinary and Life Sciences REC. The trial was approved by Wales NHS REC 3 (21/WA/0205), the Health Research Authority (HRA), Health and Care Research Wales (HCRW), university health board R&D departments in Wales, and schools in Wales and Scotland. Findings will be disseminated in peer-reviewed open-access journals, at conferences and meetings, and online to academic, clinical, and educational audiences and the wider public. Trial registration number: ISRCTN12437531.

The authors have declared no competing interest.

ISRCTN12437531

This work was supported by a National Institute for Health Research (NIHR) and Health and Care Research Wales (HCRW) Post Doctoral Fellowship programme, grant number NIHR-PDF-2018, awarded to RBJ. SS was supported by UK MRC and Scottish Chief Scientist Office core funding as part of the MRC/CSO Social and Public Health Sciences Unit Complexity in Health Improvement programme (MC_UU_12017/14 and SPHSU14) and MC-PC_13027.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Cardiff University School of Medicine Research Ethics Committee (REC) and the University of Glasgow College of Medicine, Veterinary and Life Sciences REC gave ethical approval for the pre-trial acceptability phase. The Wales National Health Service (NHS) REC 3 (21/WA/0205), the Health Research Authority (HRA), and Health and Care Research Wales (HCRW), gave ethical approval for the trial.

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

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I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable.

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All data produced in the present study are available upon reasonable request to the authors