SummaryWhat is known and objective: Polypharmacy has a significant impact on patients' health with overall expenditure on over-the-counter (OTC) medicines representing a substantial burden in terms of cost of treatment. The aim of this study, which was conducted within the framework of a European Project funded by the European Union under the Seventh Framework Programme and was entitled OTC-SOCIOMED, was to report on possible determinants of patient behaviour regarding the consumption of medicines, and particularly OTCs, in the context of primary care.Methods: A multicentre, cross-sectional study was designed and implemented in welldefined primary healthcare settings in Cyprus, the Czech Republic, France, Greece, Malta and Turkey. Patients completed a questionnaire constructed on the basis of the theory of planned behaviour (TPB), which was administered via face-to-face interviews.