Drug Utilization, Anticholinergic Burden and Predictors of Length of Stay in a Psychiatric Hospital: A Retrospective Observational Study

Background and Objectives: Mental illnesses place a substantial burden on healthcare systems and often require complex pharmacological management. However, it remains unclear whether early antipsychotic polypharmacy independently predicts length of stay after adjusting for important confounders. This study aimed to investigate drug utilization patterns, including polypharmacy and drug–drug interactions (DDIs), assess anticholinergic burden, and identify predictors of the length of hospital stay in a psychiatric inpatient setting. Materials and Methods: This retrospective, observational study was conducted at Bolu İzzet Baysal Mental Health and Diseases Hospital with 280 adult patients admitted during 2022. Medication data were extracted from electronic medical records based on medication orders within the first 72 h of admission. Potential DDIs were assessed using Lexi-Interact, and anticholinergic burden was calculated using the ACB, ADS, and ARS scales. Predictors of the length of stay (LOS) were modelled using negative binomial regression. Results: The mean age of the population was 38.65 ± 13.86 years, and 62.1% were male. Polypharmacy was present in 37.9% of patients, while antipsychotic polypharmacy was observed in 63.9%. Potential DDIs were identified in 88.9% of patients, with a significantly higher prevalence in those with polypharmacy. Mean ACB and ADS scores were high at 5.56 ± 3.32 and 4.15 ± 2.79, respectively. Multivariable regression analysis revealed that antipsychotic polypharmacy was the primary independent predictor of prolonged hospitalization, associated with a 20.9% increase in LOS (IRR = 1.209, 95% CI: 1.044–1.400, p = 0.011). While age was also statistically significant (IRR = 1.006, 95% CI: 1.001–1.012, p = 0.019), its clinical impact was minimal, representing only a 0.6% increase in LOS per year. Conclusions: Antipsychotic polypharmacy within the first 72 h of admission is a significant independent predictor of prolonged hospitalization. The high prevalence of drug interactions and substantial anticholinergic burden highlight the need for systematic early medication review. Instead of general monitoring, targeted medication therapy review focusing on antipsychotic polypharmacy in the early period of admission may be essential to identify and mitigate modifiable risk factors for prolonged hospitalization, thereby optimizing pharmacotherapy in psychiatric inpatient settings.