Problematic menstrual symptoms, such as pain, heavy bleeding, and irregular cycles, impact a high proportion of women and people who menstruate and are associated with multiple adverse physical and mental health outcomes, as well as reduced attendance and productivity at school/work. Despite this, little research has sought to identify the causes and risk factors associated with such menstrual symptoms. Socioeconomic disadvantage is one factor that has been associated with worse menstrual symptoms; however, the current evidence is mixed and unable to understand causality. It is possible that socioeconomic position (SEP) causally impacts menstrual symptoms due to early life stressors and associated lifestyle factors adversely impacting the development of the brain, the nervous system, and hormone production systems. Additionally, menstrual symptoms could negatively impact SEP through their impacts on school and work thus restricting the ability of women suffering with such symptoms to reach their fully academic and career potential. Therefore, this project aims to understand the causal, bidirectional relationship between SEP and menstrual symptoms by combining observational and genetic methods in multiple UK-based cohorts. Robust evidence that SEP and menstrual symptoms are causally related may support the need for additional support or treatment for individuals from disadvantaged backgrounds and/or provide rationale for improving school and work environments to enable women to better manage problematic menstrual symptoms.