Globally, self-medication has increased, where 25% of adults use OTC medicines. This research is intended to assess the knowledge, attitude and practice regarding OTC medicines among adults in Brunei Darussalam. An online cross-sectional survey was performed using a questionnaire adapted from similar research conducted among students in Brunei Darussalam. A total of 364 responses were collected, where the median age of the study participants was 23 years. The mean knowledge score was 7.3 out of 9, with most respondents (77.7%) having good knowledge of OTC medicines. Almost all (92.9%) showed a positive attitude towards OTC use. A statistically significant difference (p £ 0.05) was observed in attitude scores between age groups and education levels. Most of the study participants (88.2%) have practiced self-medication with OTC medicines, mainly due to their easy accessibility (79.4%). A small number practiced improper habits, such as consuming more than the recommended dose (6.0%) and not checking the expiry date (0.5%). The practice of self-medicating with OTC medicines can be advantageous when patients fully know the medications and nature of their disease. Knowledge of proper OTC medicine use among adults in Brunei Darussalam is essential to avoid improper user practices and potential health hazards associated with the misuse of medications.