Due to covid restrictions the recruitment for this study has been paused after the feasibility and acceptability data was published.

A single-centered randomized controlled trial with a parallel-groups design is utilized, comprised of mindfulness-based group therapy (MBGT) in the experimental condition, and treatment as usual (TAU) in the control condition. Participants in the experimental condition continued their regular psychiatric treatment (TAU) next to the participation in the MBGT. In order to evaluate possible psychotherapeutic effects, self-report and other clinical questionnaires including interviews and app-based assessments are evaluated before (T0), and after the four-week intervention (T1).

Ward psychiatrists identify eligible participants and invite them to participate in the study. An eligibility screening is held by the study assistant at baseline, introducing the study, providing informed consent in written form, as well as conducting the self-report measures and app-based assessments. A blinded psychiatrist who works independently of the (co-) therapist conducts the remaining rater-questionnaires. Due to the psychotherapeutic nature of the study, information about the treatment allocation had to be shared with the co-therapist and the participants. Randomization was conducted by the Random Group Generator (pubmed, 2018). The data management plan includes standard procedures for data-handling such as using anonymized identification codes for patient data. The participants have the right to access their data, and the right to claim an annihilation. The data is being stored in locked cupboards, only allowing researchers involved in the study to access the data.

Inclusion criteria:

• male and female participants
• treated as psychiatric inpatients at the psychosis - or social-psychiatric day ward
• between 18 and 65 years of age
• diagnosis of a schizophrenia-spectrum disorder according to the Diagnostical and Statistical Manual 5th edition) and the International Statistical Classification of Diseases and Related Health Problems(ICD-10) code F2
• ability to give informed consent
• willingness and ability to engage in psychotherapeutic group therapy
• low to moderate psychotic state indicated with a score of 6 < for each item at the Positive scale of the Positive and Negative Syndrome Scale (PANSS, Peralta & Cuesta, 1994)

Exclusion criteria:

• a score ≥ 6, suggesting an acute psychotic episode with severe psychotic symptoms (Peralta& Cuesta, 1994)
• acute suicidality, assessed by item eight of the Calgary Depression Scale for Schizophrenia > 1 (Addington, Addington, Maticka-Tyndale, & Joyce, 1992)
• any neurological disorders that may affect cognitive functioning
• acute substance abuse other than nicotine and prescribed medication

A blinded psychiatrist who works independently of the (co-) therapist conducts the rater-questionnaires. Due to the psychotherapeutic nature of the study, information about the treatment allocation has to be shared with the co-therapist and the participants. Randomization is conducted by the Random Group Generator (pubmed, 2018).