10 CHAPTER 1 Risk of drug-related harm in older people Reducing drug-related harm is a continuous challenge for health care professionals who aim to maintain a positive benefit-risk balance of pharmacotherapy to treat patients [1–3]. Older age, multimorbidity and polypharmacy are important risk factors for negative health outcomes related to medication use, such as adverse drug events and drug-related hospital admissions (Figure 1) [1,4,5]. This thesis focuses on the applicability of tools for medication optimisation, the effectiveness of a medication review on clinical outcomes, and the evaluation of the medication review process in hospitalised older people with polypharmacy and multimorbidity. Pharmacotherapy aims to optimise patients’ health outcomes and quality of life and to minimise drug-related harm [6,7]. Risks are inherent to medication use and can be accepted as long as the benefit-risk balance is positive [8–10], requiring considering, monitoring and evaluating the risk-benefit balance of pharmacotherapy for and together with the individual patient. In contrast, medication errors may cause potentially preventable patient harm and should be minimised. The report ‘To Err Is Human: Building a Safer Health System’ by the American Institute of Medicine in 1999 refuelled the awareness that preventable medication errors are a serious problem in health care requiring efforts to improve patient safety . Subsequent research has drawn attention to the population of older patients with multimorbidity and polypharmacy, who are particularly vulnerable to potentially preventable drug-related harm. 8.6 million unplanned hospital admissions are caused by adverse drug events in Europe each year 50% of drug-related hospital admissions in older people are potentially preventable 75% of preventable drug-related hospital admission are from patients ≥ 65 years of age and on ≥ 5 drugs Figure 1. Drug-related harm in Europe [1,4,5].