Delirium is a common and potentially preventable neuropsychiatric complication in cancer patients receiving hematopoietic stem cell transplantation (HSCT) that has profound consequences. Among cancer patients hospitalized for HSCT, delirium occurs in approximately 40% of patients and increases the risk of mortality. Long-term, delirium in this population results in worse physical health, mental health, and quality of life. Though strategies to prevent delirium have the potential to significantly improve the lives of people living with cancer, research in this area is extremely limited. Thiamine deficiency is also ubiquitous during HSCT and a known contributor to the development of delirium in other patient populations. High dose intravenous (IV) thiamine is an evidence-based and promising treatment for delirium, but no one has studied IV thiamine as a prevention strategy.