While decreased renal function is a known risk factor for hypermagnesemia caused by magnesium oxide (MgO), few studies have comprehensively investigated other contributing factors. In this study, the researchers analyzed the risk factors for hypermagnesemia development in 256 inpatients receiving MgO treatment at the Matsuyama Shimin Hospital. Multivariate analysis identified blood urea nitrogen ≧22 mg/dL, estimated glomerular filtration rate ≦43.1 mL/min, and MgO ≧1000 mg/d as risk factors. Additionally, the researchers' findings suggest a correlation between the number of risk factors and the incidence of hypermagnesemia, including the prevalence of Grade 3 cases. Interestingly, low body mass index emerged as a potential risk factor even in patients without the three identified factors. These findings highlight the importance for pharmacists to advocate for routine serum Mg level monitoring in patients with the risk factors identified in this study.