The Lowering Blood Glucose Level Effects of Cinnamon Compared to Metformin in Type 2 Diabetic Patients: A Systematic Review of Randomized Controlled Trials and Observations

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disorder with rising global prevalence and associated complications. Metformin is the standard first-line therapy, but gastrointestinal side effects have prompted interest in complementary treatments such as cinnamon (Cinnamomum spp.), which have been studied for glycemic and lipid-lowering properties. This systematic review aimed to evaluate whether cinnamon supplementation is as effective as metformin in lowering blood glucose levels in adults with T2DM and prediabetes. Following PRISMA 2020 Guidelines (Page et al., 2021) and the Academy of Nutrition and Dietetics Evidence Analysis Library checklist (Academy of Nutrition and Dietetics, 2022), electronic databases were searched for randomized controlled trials and observational studies published between 2020-2025. Ten studies met inclusion criteria, with interventions ranging from 500 mg to 10 g/day of cinnamon in capsule, extract, or dissolved powder form. Cinnamon consistently improved fasting blood glucose, HbA1c, and insulin sensitivity, particularly in overweight or insulin-resistant populations. Lipid outcomes were modest and inconsistent, with some reductions in LDL and total cholesterol. Anthropometric benefits (BMI, visceral fat) were observed in select trials but not universally. Several studies were limited by small sample sizes (n