Background People with intellectual disability (ID) are a vulnerable group in our society; many of them depend on other people for assistance in their everyday lives. Compared with the general population, people with ID have poorer general health and, therefore, need more healthcare services and use more medicines. The aim of this study is to define the population of all Finnish people with ID using administrative data and to compare their medicine use and expenditure on medicines to those of the age-matched and sex-matched controls. Methods People with ID and their age-matched and sex-matched controls (1:1) were extracted from nationwide healthcare and social allowance registers. Administrative register data on all prescription medicine purchases in 2019 were used to determine the prevalence of medicine use in both groups on a general level and by medicine categories. The differences in the prevalence of medicine use between the two groups were analysed using the logistic regression model. In addition, we studied the total expenditure on reimbursable medicine purchases covered by the National Health Insurance between people with ID and control group. ResultsThe subpopulation of people with ID consisted 37 196 individuals, of whom 82.7% purchased prescription medicines in 2019. The corresponding share of individuals purchasing prescription medicines in the control group was 70.3%. The differences in the prevalence of medicine use between the two populations were highest in the younger age groups (0-6, 7-12 and 13-17). In the study population, 28.1% (OR = 12.28; 95% CI: 11.54-13.07) of the people used antipsychotics, making it the most used medicine category in people with ID. In the control group, 3.3% of people used antipsychotics. Compared with the control group, the use of antiepileptics, drugs for constipation, mineral supplements and anxiolytics was four to seven times higher among people with ID. Furthermore, the median expenditure on medicine use among people with ID was four times higher than in the control group. Conclusions Compared with the control group, people with ID used more medicines, especially