Context The healthy ageing assumptions may lead to substantial changes in paths of aggregate healthcare expenditures, notably catastrophic expenditures of people at the end of the life. But clear assessments of involved amounts are not available when we specifically consider ambulatory care (as drug expenditures) generally offered to chronically-ill people who can remain in this health-status for a long time onward. The Government and Social Security need tools to predict the future cost of health in particular drugs expenditures taking account epidemiological changes on future. This study estimates the evolution in reimbursable outpatient drug expenditures, attributable to age structure and chronic conditions changes, of the French population up to 2029. * Methods Matched data from both the 2004 Health and Social Protection Survey (carried out by IRDES) and from French Social Security databases were used in this study. We estimate the effects of epidemiological and life expectancy changes on French health expenditures until 2029 by applying a markovian microsimulation model from a nationally representative database. The originality of these simulations holds in using an aggregate indicator of morbidity-mortality, capturing vital risk and making it possible to adapt the quantification of life expectancies by taking into account the presence of severe chronic pathologies. Three epidemiological scenarios were constructed. * Findings We forecast future national drugs expenditures, under different epidemiological scenarios of chronic morbidity: Trend scenario, healthy ageing scenario and medical progress scenario. For the population aged 25+, results predict an increase in reimbursable drug expenditures of between 1.1% and 1.8% (annual growth rate), attributable solely to the ageing population and changes in health status. * Conclusion The small difference between the healthy ageing scenario (1.1%) and the simple continuation of trends scenario (1.4%) indicates that, contrary to expectations, reduced chronic conditions of future cohorts does not imply a large saving in terms of drug expenditures.