Objective To review current literature reporting outcomes associated with utilization of the Medication Regimen Complexity Index (MRCI) with older adults in an outpatient setting. Data sources The National Library of Medicine via PubMed, International Pharmaceutical Abstracts, and the Cochrane Database were used to identify clinical trials evaluating outcomes associated with utilization of the MRCI. The medical subject heading terms "geriatrics" and "medication adherence" were used in combination with key terms "medication regimen complexity index" and "medication complexity." Study selection/data extraction Seventy-five articles met the search criteria and were reviewed. Studies were included if they had MRCI-related outcomes and were performed in patients 60 years of age and older in an outpatient setting. Eleven articles met the stated criteria. Data synthesis Higher MRCI scores may be associated with increased mortality rates, medication nonadherence, and unplanned hospitalizations; however, when compared with medication number, MRCI did not better predict increased medication nonadherence and unplanned hospitalizations. Conclusion The MRCI is a useful tool to determine medication complexity; however, current literature is limited by its observational design. Also, MRCI does not take into account potential factors such as high-risk medications and comorbid conditions, which may affect MRCI scores; therefore, additional trials are warranted before suggesting pharmacists implement this tool in their everyday practice.