Throughout history, people have reported nonordinary experiences (NOEs) such as feelings of oneness with the universe and hearing voices. Although these experiences form the basis of several spiritual and religious traditions, experiencing NOEs may create stress and uncertainty among those who experience such events. To provide a more systematic overview of the research linking NOEs with mental health, we present a systematic review of studies focusing on NOEs, well-being and mental health indicators. In a search of ProQuest and PsycInfo, we identified 725 references, of which 157 reported empirical data and were included in our review. Overall, the studies reviewed suggest that the relationship between NOEs and mental health is complex, varying according to a series of psychological and social factors. In particular, they suggest that appraisal processes play a fundamental role in the mental health outcomes of these experiences. However, we also highlight important methodological challenges such as the conceptual overlap between NOEs and well-being or psychopathological constructs, the conflation between experiences and appraisal processes in the assessment procedure, and the need for clearer assessment of the duration, controllability, impact on daily functioning and general context of the experiences. We provide a qualitative summary of empirical evidence and main themes of research and make recommendations for future investigation.
