Effectiveness of metformin treatment in the prevention of type 2 diabetes in patients with metabolic syndrome

Metabolic syndrome (MetS) is a cluster of metabolic abnormalities that significantly increases the risk of type 2 diabetes mellitus (T2DM), necessitating effective preventive strategies. This integrative review aimed to evaluate the effectiveness of metformin in preventing T2DM progression in patients with MetS. A comprehensive literature search was conducted across PubMed, Embase, LILACS, and SciELO, including studies published between 2020 and 2025. Selected studies, comprising randomized controlled trials, cohort studies, and meta-analyses, assessed metformin’s impact on T2DM incidence, fasting glucose, HbA1c, insulin resistance (HOMA-IR), and other metabolic outcomes in adults with MetS. Results from five key studies demonstrated that metformin (500–2,000 mg/day) reduced T2DM incidence by 28–92% compared to placebo or lifestyle interventions alone, with significant reductions in fasting glucose (-0.3 to -0.5 mmol/L) and HbA1c (-0.2 to -0.3%) (ZHANG et al., 2023; PATEL et al., 2023). The combination of metformin with lifestyle interventions yielded superior outcomes, particularly in obese individuals and those with higher baseline insulin resistance, with additional benefits in weight loss (-1.8 to -2.1 kg) and triglyceride reduction (-15 mg/dL) (AMER et al., 2024; PASANISI et al., 2025). Subgroup analyses highlighted enhanced efficacy in perimenopausal women with hyperandrogenism (LIM et al., 2025). Despite variability in dosing and study duration, metformin consistently demonstrated a favorable safety profile, though long-term risks such as vitamin B12 deficiency require further exploration. These findings endorse metformin as a potent preventive therapy for T2DM in MetS patients, particularly when integrated with lifestyle modifications, underscoring its potential to mitigate the global diabetes burden.