Self-medication (SM) is a global and growing phenomenon. It represents a public health problem due to antibiotic resistance, risk of adverse drug reactions, drug–drug interactions, disease masking, and increased morbidity. There is not a consensus on the definition of SM. The definitions found in different studies make it difficult to address this problem from a theoretical perspective and therefore find an adequate solution to this public health problem. The aim of this article is to search the medical literature to characterize the current understanding of SM in the medical community. We conducted a scoping review of definitions of SM by searching on PubMed – Medline, Embase, and LILACS using the following combination of keywords: ‘self-prescription’ or ‘self prescription’, ‘self-medication’ or ‘self medication’, or ‘automedication’ and ‘definition’ or ‘explanation’. The search was limited to articles containing the definition of SM, with no limit on language or year. Duplicate studies and those that did not mention the definition of SM were excluded from the final review. A total of 65 studies were included in the final selection. We found a vast heterogeneity in the definition of SM. Most articles based their definition of SM on the process of obtaining the drug, the nonparticipation of a specific health professional, the source of the medication, and the reason for SM. Other interesting concepts such as self-care, nonadherence to a prescription, reuse of stored drugs, and sharing and lending medicines were also considered forms of SM by other authors, however. This study highlights the need to reach a consensus regarding the definition of SM to adequately propose strategies to address this global health problem. This study shows the diverse concepts that need to be included in a future definition of SM. Plain Language Summary Definition of self-medication: a review with systematic methodology Self-medication (SM) is a global and growing phenomenon that represents a public health problem due to antibiotic resistance, risk of dangerous side effects, interactions between drugs, and disease masking. Currently, there is not a consensus on the definition of SM, which makes it difficult to address this problem and therefore find an adequate solution. Making a standard definition would allow the development of programs focused on addressing drug-related problems associated with self-medication behavior. The purpose of this article is to search the medical literature to define the current understanding of SM in the medical community. We included a total of 65 studies and found a great variance in the definition of SM. Most articles based their definition of SM on the process of obtaining the drug, the nonparticipation of a specific health professional, the source of the medication, and the reason for SM. Other interesting concepts such as self-care, not following a prescription, reuse of stored drugs, and sharing and lending medicines were also considered forms of SM by other authors, however. Furthermore, this study highlights that SM is a wider concept that goes beyond aiming to promote and restore health, as aesthetic and recreational purposes are also reasons for SM that can put individuals at risk and compromise the correct and safe use of medications.