Self-awareness, the capacity of becoming the object of one's own awareness, is a frontier of scientific knowledge. Over centuries, distinct philosophical and religious traditions have grappled with the subject, but only recently has the importance of self-awareness been established as a central concept for scientific investigation, to which scientific methods can be applied to explore and characterize this phenomenon. Self-awareness has important implications, notably from a clinical perspective. Psychedelics can affect the sense of self, with 'ego dissolution' being an essential feature of the experience of substances such as psilocybin and dimethyltryptamine. Recent evidence indicates that psychedelics can rearrange brain connectivity, with these changes being linked to alterations in self-awareness. Nevertheless, the extent to which specific components of self-awareness are modified by these substances has not been fully explored. It is possible that part of the clinical benefits of psychedelics, for conditions such as depression, OCD, and anxiety, is mediated by changes in self-awareness. Given this clinical potential, the current study aims to examine the effects of psilocybin on various components of self-awareness in healthy participants. 100 participants will be allocated to receive either 15mg of psilocybin (n=50) or an active placebo (100mg niacin; n=50). Participants will be assessed one week before, immediately after, and one week after the administration of the substances, performing tasks and completing questionnaires measuring self-awareness at these time points. The neural correlates of self-awareness, before and after substance effects, will be investigated using near-infrared spectroscopy. Participants allocated to the placebo group will be invited to an open-label extension with psilocybin upon availability of the substance. It is expected that the results of the study will elucidate the brain regions involved in self-awareness, as well as the alterations induced by psilocybin in this process, opening the possibility of new therapeutic interventions for different clinical groups.