Background The risks associated with over-the-counter medication are often underestimated by consumers. The incorrect use of certain medications can lead to significant patient harm. Inappropriate use can be prevented by pharmaceutical counselling. Objective To determine the number and nature of drug-related problems in over-the-counter medication with a special emphasis on high-risk over-the-counter medications. Setting Fifty-two community pharmacies in Finland. Method This observational study was conducted as a questionnaire survey. The pharmacists working in participating pharmacies documented the observed drug-related problems and pharmacy interventions in over-the-counter medication during 1 week using an electronic study form based on the Westerlund drug-related problem classification system. Main outcome measure The prevalence of drugrelated problems and problem types in different medication categories. Results The 52 community pharmacies documented 339 drug-related problems in 0.6% of over-the-counter customers, the most common problem being "Uncertainty about the indication for the drug" (39.2%). A significant proportion of the documented problems (26.3%) concerned high-risk over-thecounter medications, and the majority of these cases were associated with non-steroidal anti-inflammatory drugs (21.8%). In total, pharmacies made 641 interventions to resolve the drug-related problems. For majority of drug-related problems (87%), pharmacist's intervention involved counselling. In more than half of the problem cases, the pharmacy intervention was precautionary. Conclusion Pharmacists intervene in and prevent problems related to over-the-counter medications, including high-risk medications like analgesics, in which inappropriate use due to consumers' lack of knowledge can lead to severe consequences. As the selection and use of over-the-counter medications is continuously increasing, pharmaceutical counselling should be readily available and actively provided for consumers to achieve safer self-medication.