PURPOSE Polypharmacy in the elderly increases the risk of adverse drug reactions and leads to increased medical costs. There is little data currently available on drug modification and cost reduction during hospitalization in a geriatric unit. The aims of this study were to analyse drug modification during hospitalization in a geriatric care unit and to evaluate the repercussions in terms of cost reduction. METHODS This monocentric study included 691 patients over a period of 3.5 years. The drugs and their daily costs were counted and classified (10 classes, 37 subclasses) upon admission and upon discharge. The modifications in the number of drugs in each class and subclass, as well as their costs, were analysed. Predictive factors in drug modification between admission and discharge were investigated. RESULTS Our study showed a significant decrease in the number of drugs (mean ± standard error [SE], 5.2±0.11 to 4.5±0.07), as well as in the daily medical costs (4.4±0.18 to 3.67±0.12 €) between admission and discharge. The higher the number of drugs was upon admission, the greater the reduction was upon discharge. Cardiovascular, metabolic, analgesic and pulmonary drugs were significantly reduced, whereas gastrointestinal and anti-osteoporotic treatments increased. Diabetes, adverse drug events and the one-leg balance were predictive factors in drug modification. CONCLUSION Hospitalization in a geriatric unit allows a re-evaluation of drug management with a significant reduction in the number and cost of treatments between admission and discharge. Given the multiple consequences of polypharmacy and its serious financial impact, research to develop optimal care of the elderly and to improve medication intervention is warranted.