Adverse events related to drug therapy are a major cause of iatrogenicity. They are responsible of increased morbidity, leading to hospitalization, sometimes in emergency, and mortality, not only in ambulatory care but also during hospitalization itself. Causes are multiple : among them, confusion leading to an erroneous drug administration, mistakes regarding dosage, risks associated to self-medication, drug-drug interactions or even food-drug interactions. Elderly population is exposed to an increased incidence of drug iatrogenicity because older patients cumulate numerous risk factors, especially polypharmacy and cognitive disorders. Prevention of drug iatrogenicity is a key objective from a public health point of view. Preventive measures should target the prescriber (physician), the dispenser (pharmacist), the user (patient) and the supplier (pharmaceutical industry).