Quality of life (QoL) is a major patient reported outcome used to measure the psychological treatments success in people with schizophrenia-spectrum disorders. To date, the specific impact of different interventions on QoL remains undefined. A meta-analysis of Randomized Controlled Trials (RCTs) was carried out for this purpose. We searched Proquest, PUBMED/MEDLINE, PsycINFO, WOS, Scopus, the Cochrane Library for RCTs published until January 2023. We used multilevel meta-analysis to examine differences between intervention effectiveness of experimental and control conditions whilst accounting for data dependencies. By means of subgroup analyses, we investigated influences of intervention types (i.e. psychoeducation v. CBT v. cognitive v. combination of several types v. other, such as psychodynamic, systemic, etc.) and continuous moderators were examined with precision-weighted meta-regressions. The generalizability of results across moderators, their combinations, and analytical approaches was investigated with multiverse meta-analyses. We examined data of 60 independent studies, reporting intervention effects for objective and subjective QoL (k = 19 and 70 effect sizes based on N = 1024 and 6254 participants, respectively). Overall, psychological interventions seemed to be more effective for objective than for subjective QoL. However, specific intervention results were differentiated, suggesting largest effects of psychoeducation on objective and combined interventions on subjective QoL. Our findings suggest that QoL is a valid outcome criterion for testing intervention effectiveness, as it is sensitive to change. Additionally, psychological interventions can improve patients' QoL, though the effects are small. Further testing of less widely used interventions and a shift toward the multidimensional nature of QoL is still necessary.

Major depressive disorder (MDD), bipolar disorder (BD) and schizophrenia-spectrum disorders (SSD) are heterogeneous psychiatric disorders, which place significant burden on patient's well-being and global health. Disruptions in the gut-microbiome may play a role in these psychiatric disorders. This review presents current data on composition of the human gastrointestinal microbiota, and its interaction mechanisms in the gut–brain axis in MDD, BD and SSD. Diversity metrics and microbial relative abundance differed across studies. More studies reported inconsistent findings (n = 7) or no differences (n = 8) than studies who reported lower α-diversity in these psychiatric disorders (n = 5). The most consistent findings across studies were higher relative abundances of the genera Streptococcus, Lactobacillus, and Eggerthella and lower relative abundance of the butyrate producing Faecalibacterium in patients with psychiatric disorders. All three increased genera were associated with higher symptom severity. Confounders, such as medication use and life style have not been accounted for. So far, the results of probiotics trials have been inconsistent. Most traditional and widely used probiotics (consisting of Bifidobacterium spp. and Lactobacillus spp.) are safe, however, they do not correct potential microbiota disbalances in these disorders. Findings on prebiotics and faecal microbiota transplantation (FMT) are too limited to draw definitive conclusions. Disease-specific pro/prebiotic treatment or even FMT could be auspicious interventions for prevention and therapy for psychiatric disorders and should be investigated in future trials.