Research on disease-related malnutrition and adherence to oral nutritional supplements (ONS) has increased in recent years. To guide future studies, it is important to identify trends in terminology use and intervention characteristics. This review aimed to map characteristics of research investigating adherence to ONS in patients with disease-related malnutrition and explore changes over time. This review is a secondary analysis of quantitative studies from a systematic mixed-studies review. Online databases, including PubMed, Cinahl, Cochrane Central Register of Controlled Trials, and APA PsycInfo, were searched to identify studies published from 2000 to March 2022. A quantitative content analysis of extracted data was performed, and the Mixed Methods Appraisal Tool (MMAT) was used to assess methodological risk of bias. This review includes 137 articles, over half of which are randomized controlled trials (52%). The term “oral nutritional supplements” was used in 40% of the studies. Adherence to ONS was mainly described by the term “compliance” (69%). It was most common to offer ready-made milk-based ONS (56%) and ONS as a sole intervention (51%). The prescribed dose of ONS was fixed in 64% of studies and individualized in 22% of studies. There was variation in the methods used to assess adherence to ONS, and adherence was not reported in nearly a fifth of studies. There was an increase in methodological quality over time (p = 0.024). To ensure better understanding and increase the rigor and reproducibility of ONS intervention research, it is crucial to standardize the terminology used and to describe the interventions clearly.