A systematic review of the bidirectional relationship between psychosis and loneliness

and hypothesis: Loneliness, defined as a subjective feeling of isolation, has been significantly correlated with psychotic experiences in general and clinical populations, although less is known about the direction of this relationship. This paper aims to systematically review the longitudinal relationship between loneliness and psychosis spectrum continuum, addressing two fundamental questions: (1) is loneliness a risk factor for the development of psychosis, and (2) does psychosis increase the risk of experiencing loneliness?

A comprehensive search of 5 electronic databases yielded a total of 4386 records, from which 10 observational studies were finally included.

Six studies investigated the first research question, and all of them identified a significant association between loneliness and the subsequent incidence of psychosis (question 1). Conversely, 4 studies explored the second research question, with 3 suggesting that individuals within the psychosis spectrum may face heightened susceptibility to loneliness (question 2). The remaining study, conducted during the COVID-19 pandemic, did not yield significant findings. Assessment of methodological quality indicated predominantly moderate-to-high-quality studies.

The findings underscore the need for further research, particularly longitudinal prospective studies, to clarify whether the observed association between loneliness and psychosis is direct or whether it is instead moderated or mediated by other variables. Overall, the available evidence provides stronger support for loneliness as a potential risk factor for the onset of psychosis, although the number of longitudinal studies addressing this question remains very limited. Addressing these gaps in knowledge could inform the development of targeted prevention programs and interventions for people with psychotic spectrum disorders.