A standardized medication plan (MP) was recently enacted into German law (§ 31a SGB V). The purpose of our study was to assess if patients with chronic diseases requiring polymedication understand the standardized MP and can transfer the given information into practice. 100 patients who took at least five medicines regularly were prospectively included in a cross-sectional study: 50 patients with the primary diagnosis chronic heart failure (CHF), and 50 with diabetes mellitus type 2 (DMT2). We performed a structured test-scenario studying the handling of a provided MP then evaluated the execution of the information on the MP by filling pill boxes and requested patients' opinion. An established weighted scoring system, the "Evaluation Tool to test the handling of the Medication Plan" (ET-MP) was applied to quantitate the ability of the patients to handle the MP. In addition, signs of depression, cognitive function and self-care behavior in chronic heart failure were characterized using the PHQ-9, Mini-Cog, and G9-EHFScB-9 questionnaires, respectively. The understanding of the MP was poor and irrespective of the underlying primary diagnosis. Only 32% of all patients were able to handle the MP without difficulties (ET-MP score >90%), the median ET-MP score was 83 [(IQR) 50-98]. Comprehension of the MP was better in patients aged <70 years compared to ≥70 years (p<0.01). Patients ≥10 years of education achieved higher ET-MP results than patients with <10 years of education (p<0.01). Patients with signs of cognitive impairment exhibited significantly lower ET-MP scores than patients without cognitive impairment (p<0.001). There were no significant correlations of the ET-MP score with number of daily medications, living situation, sex, the Charlson Comorbidity Index, the PHQ-9 score, and use of a dosing aid or possession of a medication list.