BACKGROUND: Obesity and physical inactivity are associated with several diseases such as diabetes, cardiovascular diseases, musculoskeletal complaints, osteoporosis, certain types of cancer and depression. However, few data are available on the speific types of medication associated with obesity and physical inactivity. OBJECTIVE: The aim of this study was to determine the independent association of body mass index (BMI) and physical inactivity with use of specific classes of prescription drugs, and the interaction between BMI and physical inactivity. METHODS: The Doetinchem Cohort Study is a population-based longitudinal study. We analyzed cross-sectional data of 1703 men and 1841 women, examined between 1998 and 2002, for whom drug-dispending data were available from the PHARMO database. Drugs were coded according to the WHO Anatomical Therapeutic Chemical (ATC) classification system. Body weight was measured during the physical examination. Physical activity was assessed using an extensive questionnaire. Persons were defined as a user of a certain drug class if they filed at least one prescription in the year around (+/-6 months) the examination. RESULTS: Compared with normal weight persons (BMI 18.5-25 kg m(-2)), obese persons (BMI>30 kg m(-2)) had a higher use of prescription drugs of several drug classes, especially cardiovascular drugs (OR (95% CI): 3.83 (2.61-5.64) in men and 2.80 (2.03-3.86) in women) and diabetes drugs (OR (95% CI): 5.72 (2.32-14.14) in men and 3.92 (1.80-8.54) in women). In women, physical inactivity was also associated with higher use of certain drug classes, such as drugs for blood and blood-forming organs (OR (95% CI): 2.11 (1.22-3.65)) and musculoskeletal drugs (OR (95% CI): 2.07 (1.45-2.97)), whereas in men this was not the case. We found no interaction between BMI and physical inactivity with respect to use of prescription drugs. CONCLUSION: In both men and women, obesity was associated with a higher use of several types of prescription drugs, whereas physical inactivity was only associated with a higher use of certain drug classes in women.