For technology to contribute to organizational performance, an essential prerequisite is not just adoption but full utilization by its users. Understanding IT assimilation is particularly important in the contexts where system use is mandatory. This paper examines factors affecting the assimilation of electronic medication management system (eMMS) at the individual level in a hospital setting where the use of eMMS is mandatory. Drawing on literature in IT assimilation, a re-search model was proposed with both organizational (direct supervisor, job specification, and performance evaluation) and cognitive factors (intrinsic motivation, absorptive capacity, and perceived usefulness) that are hypothesized to have impacts on width and depth of eMMS assimilation. The model was tested with survey data from 196 eMMS users in a public hospital. The results show that factors have different effects on width and depth of eMMS assimilation for different user groups. Specifically, it was found that nurses with more absorptive capacity are more deeply and widely assimilated. For doctors, their direct supervisors and intrinsic motivation influence their depth of assimilation. Interestingly, nurses with more favorable perception of usefulness have assimilated more deeply, whereas more deeply assimilated doctors are those with less favorable perception of usefulness.