Purpose: To conduct a randomized controlled pilot study investigating the use of high dose intravenous (IV) thiamine to prevent delirium and mitigate the long-term effects of delirium, including health-related quality of life (HRQOL), functional status, and neuropsychiatric outcomes, in patients admitted to University of North Carolina (UNC) Hospital for allogeneic hematopoietic stem cell transplant (HSCT).