The primary objective of this study was to investigate the impact of RMMRs on medication regimen complexity, as assessed by a validated measure.Retrospective analysis of RMMRs pertaining to 285 aged care residents aged ≥ 65 years in Sydney, Australia. Medication regimen complexity was measured using the Medication Regimen Complexity Index (MRCI) at baseline, after pharmacists' recommendations (assuming that all of the pharmacists' recommendations were accepted by the General Practitioner (GP)), and after the actual uptake of pharmacists' recommendations by the GP. Differences in the regimen complexity was measured using the Wilcoxon sign rank test.Pharmacists made 764 recommendations (average 2.7 recommendations per RMMR), of which 569 (74.5%) were accepted by GPs. The median MRCI at baseline in the sample was 25.5 (IQR = 19.0-32.5). No statistically significant differences were demonstrated in the MRCI scores after pharmacists' recommendations (p = 0.53) or after GPs' acceptance of these recommendations (p = 0.07) compared to the baseline.Our study revealed high acceptance of pharmacists' recommendations by GPs. This suggests that RMMRs are useful for identifying and resolving drug-related issues among residents of ACFs. However, our study failed to show a significant effect of RMMRs in reducing the medication regimen complexity, as measured by the MRCI. Further studies are needed to establish the association of medication regimen complexity and clinical outcomes in residents of ACFs.