Shared decision making (SDM) about medicine with older poly-medicated patients is vital to improving adherence and preventing medication-related hospital admissions, but it is difficult to achieve in practice. This study’s primary aim was to provide insight into the extent of SDM in medication decisions in the Emergency Department (ED) and to compare how it aligns with older poly-medicated patients’ preferences and needs. We applied a mixed-methods design to investigate SDM in medication decisions from two perspectives: (1) observational measurements with the observing patient involvement (OPTION 5) instrument of healthcare professionals’ SDM behavior in medication decisions and (2) semi-structured interviews with older poly-medicated patients. A convergent parallel analysis was performed. Sixty-five observations and fourteen interviews revealed four overall themes: (1) a low degree of SDM about medication, (2) a variation in the pro-active and non-active patients approach to conversations about medicine, (3) no information on side effects, and (4) a preference for medication reduction. The lack of SDM with older patients in the ED may increase inequality in health. Patients with low health literacy are at risk of safety threats, nonadherence, and preventable re-admissions. Therefore, healthcare professionals should systematically investigate older poly-medicated patients’ preferences and discuss the side effects and the possibility of reducing harmful medicine.