OBJECTIVES: Anxiety and hypnotic medications are commonly used for elderly patients but are potentially inappropriate and need more attention. Medication regimen complexity index (MRCI) provides method to evaluate the complexity of medication using factors beyond the medication count. This study aimed to use the MRCI to explore the complexity of all medications used by elderly patients taking anxiety-hypnotics prescriptions. METHODS: This retrospective cohort study was piggy-backed under an ongoing sleep-medicine project in Taiwan. The first 60 patients from this larger study conducted in an academic medical center in Taiwan were included. The difference between MRCI score and medication count within patients with anxiety-hypnotic disease and other comorbidities. The score was calculated at baseline at one month later. The demographic, disease status, and corresponding MRCI scores were compared to or medication counts using appropriate t tests and chi-square test. RESULTS: Baseline characteristics, total MRCI, and MRCI section score were comparable between both sexes and all ages on the first date of visit, but females were older than males. Total MRCI, and medications requiring additional instruction were higher during one-month follow up, especially among male elderly. Higher MRCI scores were related to factors other than anxiety-hypnotic prescriptions. Additional medication-use instructions accounted for the majority of anxiety-hypnotics related MRCI score. Frequency of use accounted for the majority of other comorbidity MRCI scores. CONCLUSIONS:  Anxiety-hypnotic medications did not have a large effect on the MRCI. A difference in MRCI score existed over one-month, and changes in regimen complexity for anxiety-hypnotics and other medications in the elderly should be continuously monitored and evaluated over time to ensure safe medication use in the elderly.