All forms of dementia, particularly Alzheimer’s disease, are increasing in line with population ageing. In this population, there are few data available regarding the prevalence and risk factors of adverse drug reaction (ADR). For this reason, one of the measures of the French government initiative for Alzheimer’s disease for the period 2008–2012 was to improve the state of the knowledge on ADR in this population. The aims of this PhD thesis were to describe ADRs, drug suspected in the occurrence of these ADRs and to identify the risk factors for the occurrence of ADR in older subjects hospitalised in an acute geriatric medicine ward specialised in the management of patients with dementia syndrome. An ad hoc study was conducted in this population. This study was completed by data from Regional Pharmacovigilance Center of Champagne-Ardenne and a systematic review of the literature. Caution is needed when prescribing angiotensin-converting enzyme inhibitors/angiotensin II receptor blockers, neuroleptics, antidementia drugs, or certain types of antiarrhythmics in patients suffering from dementia. Our findings underline the importance of taking into consideration the characteristics of the patients when prescribing drugs in this specific population. Early detection of dependency in cognitive impaired subjects and the implementation of home help could help to avoid ADRs related to errors in taking medications.