ObjectiveThe number of published systematic reviews has exploded in the past three decades, followed by a large number of overlapping systematic reviews on the same topic. We aim to review the frequency and causes of overlap in systematic reviews.MethodsFollowing PRISMA 2020 guidelines, we searched PubMed and Embase from inception to March 4, 2024, to identify English-language studies quantitatively assessing overlapping systematic reviews on the same topic. Nonempirical studies and duplicates were excluded. Two researchers independently screened and extracted data, with results analyzed descriptively.ResultsEleven quantitative studies were included in this study. Findings revealed that 68% of systematic reviews exhibited overlap, with a maximum of 76 overlapping reviews identified on a single topic. Only 36% overlapping systematic reviews referenced previous studies and a mere of 9% reported protocol registrations. The most mentioned causes for overlap were the omission to reference previous systematic reviews (6; 55%), lack of protocol registration (3; 27%), performance-driven incentives among researchers (3; 27%). Key recommendations to mitigate overlap included mandatory protocol registration (7; 64%), explaining the novelty and innovation of research (5; 45%), strengthening the review of overlap (3; 27%).ConclusionOverlapping systematic reviews undermine evidence reliability due to transparency gaps and methodological weaknesses. Mandatory protocol registration, interdisciplinary collaboration, and adherence to tools like AMSTAR 2 are critical to curb redundancy. Journals must enforce rigorous quality checks and support living reviews. Stakeholders urgently need to standardize definitions of overlap, establish update frameworks, and promote ethical research practices. Addressing these challenges will enhance the efficiency and trustworthiness of evidence synthesis in healthcare.