Abstract Introduction Older patients on polypharmacy are predisposed to drug‐related problems (DRPs). While medication therapy management (MTM) with pharmacist involvement can reduce DRP occurrence, few have examined its impact on reducing unplanned admissions. This study was designed to determine whether a pharmacist‐provided MTM service can reduce unplanned admissions through the comparison with patients receiving usual care. Methods A retrospective case–control study was conducted in Changi General Hospital. Patients enrolled to MTM service from January 2016 to December 2021 were included in the intervention arm ( n  = 96) while patients who were not enrolled were recruited as control ( n  = 96). Primary outcome was the incidence rate ratio (IRR) of unplanned admissions within 6 months postindex visit comparing between intervention arm and control arm. Secondary outcomes included number of DRPs identified, types of DRPs, and the potential risks avoided by resolving DRPs. The negative binomial mixed model was used to model the unplanned admissions data. Results MTM with pharmacists' involvement was associated with a 39% (IRRs 0.61, 95% confidence interval CI 0.37–0.99, p  = 0.047) lower rate of admissions in the intervention compared with the control group. There were higher number of DRPs (144 vs. 2) found in the intervention arm compared with control arm, respectively. The most prevalent types of DRPs were “Nonadherence” (80.1%), “Drug omission” (5.6%), and “Inappropriate dose” (2.8%). The most common potential risks avoided were increased cardiovascular risk, n  = 29 (22.1%), increased fall risk, n  = 18 (13.7%), and increased fracture risk, n  = 17 (13.0%). Conclusion The study suggests that pharmacist‐provided MTM service decreased unplanned admission. It has improved medication safety and quality of care by identifying and resolving more DRPs.