This randomized controlled trial (RCT) with 250 patients suffering from type 2 diabetes mellitus (T2DM) aims to investigate the effectiveness of the self-guided digital therapeutic covivio. Inclusion criteria are: male, female or non-binary; age ≥ 18 years; confirmed diagnosis of T2DM; elevated levels of diabetes-specific emotional distress (Problem Areas in Diabetes [PAID]-20 score ≥ 33); consent to participate; sufficient German language skills. Exclusion criteria are: a diagnosis of type 1 diabetes mellitus (T1DM); current use of continuous glucose monitoring (CGM) as part of one's diabetes treatment; changes or planned changes in medication within 4 weeks before the baseline visit or in the subsequent 6 months; a bariatric operation within 4 weeks before the baseline visit or such an operation planned in the subsequent 6 months; changes or planned changes in psychotherapeutic treatment within 4 weeks before the baseline visit or in the subsequent 6 months. In addition, participants will be excluded from the study if they did not wear the CGM sensor for at least 6 of 7 days at baseline (before randomization), providing a minimum of 96 hours of glucose values including at least 24 hours overnight.

Patients will be randomized and allocated in a 1:1 ratio to either an intervention group, in which they will receive access to covivio in addition to treatment as usual (TAU, n = 125), or to a control group, in which they will receive only TAU (n = 125).

Co-primary endpoints of this trial will be the between-groups difference in the PAID-20 total score in the intervention and control group at six months, adjusted for the PAID-20 baseline score as well as the glucose management indicator (estimated HbA1c) assessed using continuous glucose monitoring devices (for a period of 7 days) at six months, adjusted for the baseline score.

Secondary endpoints will be diabetes self-management skills, body mass index (BMI), and quality of life.

Inclusion Criteria:

• male, female or non-binary
• age ≥ 18 years
• diagnosis of T2DM secured via submission of a medical certificate attesting to the presence of at least one of the following ICD-10-GM diagnoses of T2DM: E11.20, E11.30, E11.40, E11.50, E11.60, E11.72, E11.74, E11.80, E11.90
• elevated levels of diabetes-specific emotional distress: cut-off ≥ 33 on the PAID-20
• access to CGM-compatible smartphone
• consent to participate
• sufficient knowledge of the German language

Exclusion Criteria:

• diagnosis of type 1 diabetes mellitus (T1DM)
• change in medication (type, frequency of use or dosage) within 4 weeks before the baseline visit or planned within the subsequent 6 months
• recent or planned bariatric operation within 4 weeks before the baseline visit or within the subsequent 6 months
• change in psychotherapeutic treatment within 4 weeks before the baseline visit or planned within the subsequent 6 months
• current use of continuous glucose monitoring (CGM) as part of one's diabetes treatment
• experiencing problems with the CGM sensor or insufficient CGM data quality at baseline (T0) (i.e., wearing the CGM sensor on less than 6 of 7 days, providing less than a minimum of 96 hours of glucose values, providing less than 24 hours overnight CGM data)