Background In management of type 2 diabetes, autonomy supporting interventions may be a prerequisite to achieve 'real life' patient engagement and more long-term improvement. Preliminary evidence has previously shown that the autonomy supporting intervention, guided self-determination method might have effect on HbA1c and diabetes distress in people with type 1 diabetes. However, previous trials were all rated as high risk of bias and did not assess potential harm of the the intervention. Thus, in the current trial, the objective is to investigate the benefits and harms of guided self-determination interventions versus an attention control group intervention in adults with type 2 diabetes.

Methods/design The trial planned is a randomised, pragmatic, investigator-initiated, dual-centre, parallel group, clinical superiority trial of guided self-determination intervention versus an attention control group for people diagnosed with type 2 diabetes in outpatient clinics. The participants (n=224) will be recruited from the department of Endocrinology at a University hospital of Copenhagen, the Capital Region of Denmark and from Steno Diabetes Center Odense, University hospital in the Southern Region of Denmark. The experimental stepped-care intervention will consist of 3-5 analogue or digitally provided guided self-determination sessions lasting up to one hour with a guided self-determination facilitator. The attention control group will receive similar number of sessions lasting up to one hour with a communication trained healthcare professional provided face-to-face, digitally, or over telephone.This trial protocol is guided by the SPIRIT and CONSORT guidelines. Participants will be included if they have type 2 diabetes, > 18 years old, and, are not pregnant. Participants will be assessed before randomisation, at 5- and 12-months follow-up. The primary follow-up timepoint will be 12-months follow-up. The primary outcome will be diabetes distress. Secondary outcomes will be quality of life, depressive symptoms, and adverse events not considered serious. Exploratory outcome will be glycated haemoglobin, motivation, and serious adverse events. Data will be collected using REDCap. The analyses will be performed using the statistical programme Stata version 16.

Inclusion Criteria:

• >18 years of age.
• Diagnosed with type 2 diabetes ≥ 3 months according to the International Classification System of Diseases (ICD-11.2-11.9) [43].
• Signed informed consent

Exclusion Criteria:

• Pregnancy
• Prior participation in GSD course(s) for the past two years
• Lack of signed of informed consent

According to the International Committee of Medical Journal Editors (ICMJE), a detailed data sharing plan is a requirement. We adhere to the requirements with the following statements: Depersonalised individual patient data will be made available to increase transparancy and use of data. Immediately following publication the Trial Protocol, Statistical Analysis Plan, Informed Consent Form, Clinical Study Report, Analytic Code will be made available through a link for anyone who wishes to a access data. There will be no end date for this access.

Immediately following publication the Trial Protocol, Statistical Analysis Plan, Informed Consent Form, Clinical Study Report, Analytic Code will be made available through a link for anyone who wishes to a access data

There will be no end date for this access.

Participants and treatment providers will not be blinded to the allocated trial intervention. The treatment providers are not involved in the analyses. All other medical personnel will be blinded by blinding of notes in the participant's electronic records. Outcome assessors and external statisticians at the Copenhagen Trial Unit will be blinded to the randomisation status of the participants. The statistical analyses will be conducted with the intervention groups coded as X and Y. The steering committee will write two abstracts while the blinding is intact, one assuming the experimental intervention group is X and the control intervention group is Y, and one assuming the opposite. After this, the code will be broken.