Participants randomized into the experimental condition attend MBGT for four weeks in addition to regular university hospital outpatient treatment as usual (TAU). Overall, the core modules of the program are based on mindfulness-based cognitive therapy, taking into account both Chadwick's recommendations for implementing mindfulness in psychosis as well as patient feedback. Each week, a new topic is introduced to enhance the understanding of four core aspects of mindfulness (breath, senses, detachment, and body awareness). The therapy sessions will be held by a psychotherapist in training in cognitive behavioral therapy with over three years of experience in mindfulness practice and supervised by a psychotherapist with more than a decade of experience in mindfulness-based therapeutic approaches. Within the sessions, short periods of meditation are used to avoid prolonged periods of silence, and basic anchoring techniques and easy-to-understand language are used.

All participants will be recruited from the outpatient facility at the Charité - Universitätsmedizin Berlin, Campus Benjamin Franklin and therefore, the heterogeneity of the obtained treatment options can be limited. As the standard procedure in our outpatient facility, patients will be seen monthly by a psychiatrist as well as individual sessions by a psychotherapist or psychiatric nurse (1:2 ratio). Hence, regardless of the study condition, all participants will obtain high standard health care at a renowned university hospital outpatient facility according to official national and international treatment guidelines providing pharmacological therapy, psychological consultation, and, on-demand, psychosocial support by social workers. The amount of psychotherapy received and on-demand psychosocial support will be recorded during the study period.

see above

Venous blood samples will be taken to determine the basal oxytocin plasma to obtain an individual baseline and comparison level. Furthermore, saliva samples will be taken before and after each MBGT session to determine OXT levels.

Interpersonal Reactivity Index (IRI)

The IRI measures empathy on four subscales: perspective taking, fantasy, empathic concern and personal distress. Each subscale consists of 4 items rated on a 7-point Likert scale. The internal consistent is satisfactory with a Cronbach´s alpha of .78.

Empathy Quotient (EQ)

The EQ consists of 40 statements to which participants have to indicate the degree to which they agree or disagree. There are four response options: 'strongly agree', 'slightly agree', 'slightly disagree', 'strongly disagree'. 'Definitely agree' responses score two points and 'slightly agree' responses score one point on half the items, and 'definitely disagree' responses score two points and 'slightly disagree' responses score one point on the other half. The remainder of the response options score 0.

Finally, Cronbach's alpha was 0.92, which is high.

The SMQ comprises 16 items that are rated on a seven-point Likert-scale ranging from (6) "agree totally" to (0) "disagree totally". Consequently, the total score ranges from 0 to 96, with a higher score indicating higher mindfulness. The internal consistency of the German version of the SMQ was Cronbach's α = 0.89.

We investigate whether polygenic risk scores (PRS) for empathy can predict empathy scores across groups at baseline in individuals with schizophrenia. For this purpose, the subject's genotypes will be examined. PRS have been shown to be associated with complex genetic traits such as empathy and mental disorders such as schizophrenia or autism spectrum disorders. Moreover, we will investigate whether empathy-PRSs and specific genetic configurations in the OXTR are associated with MBGT outcomes and OXT levels in blood samples on an exploratory level.