The Impact of CGM on Glycemic Control in Diabetes Patients – A Review of Recent Studies

Background: Continuous glucose monitoring (CGM) has advanced rapidly and is now used beyond type 1 diabetes (T1D). New randomized controlled trials (RCTs), meta-analyses, and updated international guidelines from 2020 to 2025 have reshaped clinical use, which warrants an updated narrative synthesis. Objective: To provide a narrative review of recent clinical evidence on CGM, compare effectiveness across diabetes populations, appraise the strength and limitations of the evidence, and identify priorities for future research. Methods: Thirty-five publications were included after targeted searches in PubMed, ClinicalTrials.gov, and official diabetes organization websites, with the last search on 1 August 2025. Eligible English language studies reported clinical outcomes, accuracy, usability, or implementation in adults with T1D or type 2 diabetes (T2D). Selection and data extraction were performed manually. Findings were synthesized descriptively. No meta-analysis or formal risk of bias assessment was performed. Results: In T1D, randomized trials and reviews consistently showed improvements in hemoglobin A1c (HbA1c), time in range (TIR), and fewer hypoglycemic events, including a mean HbA1c reduction of 0.27 percent with closed loop systems. In insulin treated T2D, effects on HbA1c ranged from minus 0.74 to minus 0.20 percent, with variable improvements in TIR. Time spent in hypoglycemia decreased by about 0.66 percent. In one trial insulin dose fell by 10.6 units per day and weight by 3.3 kilograms. Evidence for non-insulin treated T2D, older adults, and pregnant women remains preliminary but suggests potential benefit. Patient reported outcomes indicated moderate gains in treatment satisfaction, sleep, and daily functioning, with high adherence in older adults reported at about 93 percent. Conclusions: The evidence is strongest for T1D and supportive though heterogeneous for insulin treated T2D. For non-insulin treated T2D, older adults, and pregnant women, current data are limited and do not yet support firm recommendations. Future studies should address long term outcomes, cost effectiveness, and the role of CGM in underrepresented populations to guide clinical practice.