This review examines generative artificial intelligence (GenAI) in English-medium instruction (EMI) in higher education and implications for Vietnam. ERIC, Crossref and supplementary searches covered English-language empirical journal articles from January 2020 to 16 October 2026. Two reviewers screened records (κ = .86); 18 studies were synthesised thematically and considered using MMAT 2018, although only ten had full-text access and eight were available through abstracts or titles. GenAI mainly supported writing and language access. Reported benefits included easier comprehension, lower anxiety and time savings; two cross-sectional studies linked use with academic outcomes. Risks included dependence, distorted disciplinary meaning, integrity concerns and insufficient guidance. The largely perceptual evidence did not establish effects on content learning. A scaffolding perspective suggests evaluating Vietnamese pilots combining lecturer development, purposeful bilingual tasks, institutional guidance and process-based assessment, with planned withdrawal of support.