Metadiscourse markers (MDMs) are rhetorical devices used to enhance audience comprehension (interactive MDMs) and engage authors and audiences within a text (interactional MDMs). This study examines diachronic variation in the use of interactive and interactional MDMs across 240 research articles (RAs) from soft-pure (English literature), soft-applied (applied linguistics), hard-applied (pharmacology), and hard-pure (mathematics) disciplines, published in two periods (1994–1998 and 2019–2023). Using descriptive and inferential statistics, along with commentary on corpus excerpts, the results revealed distinct patterns of diachronic changes in MDM use, confirming temporal and disciplinary variations. Based on the findings, the study provides recommendations for English for academic purposes (EAP) and reading and writing courses. Additionally, suggestions for future research on this underexplored variation are offered.