This study examined patients' experiences of menstrual health in psychiatric inpatient settings in England as reported by staff and patients. Questionnaires were conducted with 67 staff members and 101 people with lived experience of menstruation and treatment on a psychiatric ward. 10 semi-structured interviews were conducted with people with lived experience. Data were analysed using reflexive thematic analysis. Grouped into overarching themes of institutional and interpersonal environments, four themes were identified: access to menstrual materials; the lack of privacy when menstruating in psychiatric inpatient settings; attitudes and approaches to menstruation; and menstrual support needs and care provision. There was variation among the experiences reported, with some patients receiving dignified care, whilst others described facing 'degrading' and 'dehumanising' treatments and enhanced feelings of shame and embarrassment around menstruation, in comparison with what they usually experience. This appeared to arise due to the interplay between mental health services overlooking menstruation and the overreliance on restrictive practices. These experiences may be understood as menstrual injustices, period poverty,potentially amounting to neglect and posing iatrogenic harms. Participants also discussed how their mental illness and distress, particularly within the context of trauma and/or eating disorders, shaped their menstrual experiences. However, many patients did not receive adequate support in relation to this. Patients' pain and disorder related to menstruation, or gynaecological conditions, was often described as being dismissed by staff or being viewed as beyond the responsibility of mental health services. This study highlighted the urgency for actions to be taken to provide greater support for patients who menstruate in psychiatric inpatient settings.