Aligned with the NIMH 2023 Strategic Plan, which highlights suicide prevention and digital health as research priorities, the proposed project is consistent with NIH’s strategic goal to examine mental illness trajectories across the lifespan. The proposed project utilizes high-resolution digital health sleep data in a clinical trial to identify periods of acute suicide risk and potential sleep-related treatment targets, while also examining the impact of the menstrual cycle in these processes. Suicide is a leading cause of death, and it is important for ongoing studies to focus on when patients may be at imminent risk. Emerging research suggests the menstrual cycle and sleep disturbances are time-varying modulators of acute depression and suicidality. The primary mentor’s prior work substantiates a link between cyclical changes in ovarian steroids and suicidality and confirms that most patients recruited for recent suicidal ideation (SI) demonstrate perimenstrual worsening of SI. Further, the laboratory’s two crossover RCTs demonstrate that natural perimenstrual steroid withdrawal serves as a recurring trigger for worsened suicidality and depression that can be reversed with E2+P4 supplementation. However, treatment of this kind is not feasible long-term due to clotting and hormone-dependent cancer risks, so it is critical to identify physiological mediators of these effects which may be treatment targets. Sleep disturbances also predict acute increases in suicidality/depression and there is within-person worsening in sleep perimenstrually suggesting that sleep may be a time-varying physiological mediator for the relationship between the cyclical hormones and suicidality in some people. The proposed study will utilize archival data from the primary mentor’s recently completed R01-funded RCT, which the candidate was instrumental in collecting, in 150 AFAB transdiagnostic patients with suicidality, including 1-3 months of daily surveys, hormonally confirmed cycle phases, and wearable sleep data (Oura ring), to evaluate the role of sleep in perimenstrual exacerbation of SI/depression. The proposed study has several novel aspects: 1) High temporal resolution sleep data across long observation periods; 2) Analytic methods that consider individual differences in cyclical hormone sensitivity and sleep patterns; 3) Experimental ovarian hormone manipulation to establish causality in the relationship between sleep disturbances, cycling hormones, and suicidality/depression. The proposed project will provide clinical trial research experience, training in nomothetic and idiographic statistical modeling, and collaborative mentorship in methods and clinical exposure in sleep and reproductive psychiatry to help the candidate achieve long-term career goals in academic medicine.