Hematopoietic stem cell transplant (HSCT), also known as bone marrow transplantation, is a therapeutic procedure that revolutionizes the treatment landscape for various debilitating conditions, including hematological malignancies and genetic disorders. Busulfan, an alkylating agent, plays a pivotal role in this regimen by eradicating malignant tumor cells and replacing unhealthy cells with healthy ones. In recent years, therapeutic drug monitoring (TDM) has emerged as a valuable tool for optimizing the dosing strategies of busulfan-based regimens in adult HSCT patients. This narrative review aims to comprehensively assess the clinical relevance and significance of TDM explicitly about busulfan-based regimens in adult HSCT patients. This review explores and analyzes existing literature, focusing on the efficacy, safety, and practical implications of utilizing TDM to optimize busulfan dosing strategies in this patient population. A review of English written literature on PubMed, Google Scholar, and Cochrane Library was performed on the terms "busulfan and pharmacokinetics" and "transplant and conditioning". The evidence is presented first on factors influencing Busulfan clearance and volume distribution. Then, the need to implement TDM of busulfan-based regimens in adult patients is discussed. A large-scale trial is required to demonstrate the benefit of anticipating and avoiding Adverse Drug Reactions and sufficient dosage to reach desired objectives. Future research on TDM of busulfan-based regimens in adult HSCT patients must address several critical issues.