A rater-blinded randomized controlled trial with a parallel-group design is utilized, comprised of yoga-based group intervention (YoGI) in the experimental condition, and treatment as usual (TAU) in the control condition. The participants in the experimental condition participate in YoGI beside their regular psychiatric treatment (TAU). The intervention is designed for in-patients with schizophrenia spectrum disorders. With the aim of examining the feasibility, acceptability and effectiveness, self-report and blinded rater-based assessments are evaluated before the YoGI (T0), and after four weeks of taking part in intervention (T1).

Building on the results of the feasibility and acceptability trial, the study is now progressing to a full randomized controlled trial. The primary outcome for the full trial will be positive symptoms of schizophrenia spectrum disorders, assessed by a blinded rater using the Positive and Negative Syndrome Scale (PANSS). The target sample size has been adjusted to ensure sufficient statistical power, and the trial will evaluate secondary outcomes, including (body) mindfulness, negative symptoms, cognitive functioning, and quality of life, and stress. This study aims to provide robust evidence for the effectiveness of YoGI in comparison to treatment as usual (TAU).

Psychiatrists and psychologists at the ward for psychotic disorders 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 electronic consent, as well as conducting the self-report measures and app-based assessments. A blinded psychologist who works independently of the (co-) psychologist 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-psychologist and the participants. Saliva samples are also taken to examine stress-related biomarkers. 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 saved in an online database, only allowing researchers involved in the study to access the data.

Inclusion Criteria:

• male and female participants
• treated as psychiatric inpatients at the psychosis ward or in the social-psychiatric day clinic
• ≥18 years
• 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
• conflicting co-therapy such as electroconvulsive therapy or ketamine treatment

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