Antipsychotic drugs are used to treat a range of psychiatric disorders including schizophrenia, bipolar disorders, and psychotic depression. Most antipsychotics are associated with significant weight gain and metabolic disturbances, which increase the risks for other diseases (obesity, diabetes, coronary diseases, etc.) and negatively impact medication adherence and quality of life. Evidence has shown that Olanzapine, for example, increases appetite, food intake, and food reward and modulates the gut microbiota. The gut microbiota can modulate adiposity, metabolism and immune-endocrine signals that impact host's energy balance and feeding behaviour. This, together with the fact that antipsychotic-induced remodelling of the gut microbiota has been associated with weight gain, suggests that microbiota-targeted interventions could help to alleviate or prevent the distressing side-effects of antipsychotic medications. The investigators have previously published promising data demonstrating anti-obesity effects of a novel Bifidobacterium longum APC1472, in a mouse model of obesity and in an overweight/obese population of humans, reducing levels of glucose and normalizing ghrelin levels. Because atypical antipsychotic medications are often used in people experiencing psychosis and the mechanisms of antipsychotic-induced weight gain and metabolic dysfunction have been suggested to include glucose intolerance (hyperglycaemia) and aberrant ghrelin signalling, the investigators propose to assess if adjunct supplementation of Bifidobacterium longum APC1472 can attenuate weight gain and metabolic side-effects associated with the use of atypical antipsychotic medication in people with non- affective psychosis. The investigators propose an exploratory patient-oriented research study, to assess the potential of adjunct Bifidobacterium longum APC1472 supplementation in individuals with psychosis receiving antipsychotic treatment, to ameliorate the liability to gain weight and/or normalize metabolic disturbances. Findings from this study will support clinical decision-making, increasing patient choice, and increase medication adherence, which will ultimately improve health and quality of life, and overall wellbeing of individuals as they pass through normal life stages.