Efficacy and Safety of Syzygium cumini and Related Myrtaceae Interventions for Dysglycemia: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background: Syzygium cumini and other Myrtaceae plants are widely used as traditional remedies for dysglycemia, yet clinical evidence remains fragmented and heterogeneous. This study aimed to evaluate the efficacy and safety of S. cumini and related Myrtaceae interventions in individuals with dysglycemia. Methods: A systematic review and meta-analysis of randomized controlled trials was conducted in accordance with PRISMA 2020 and registered in PROSPERO (CRD420261332539). PubMed, Scopus, Embase, MEDLINE, and Web of Science were searched from inception to 3 September 2025. Eligible trials enrolled participants with type 2 diabetes mellitus (T2DM) or prediabetes and evaluated Myrtaceae interventions versus controls. Random-effects meta-analyses were performed to estimate mean differences (MDs) with 95% confidence intervals (CIs). Results: Thirteen trials comprising 802 participants were included. Myrtaceae interventions were associated with a statistically significant but modest reduction in fasting plasma glucose (MD −14.40 mg/dL, 95% CI −23.12 to −5.67; I2 = 98.57%). However, effects on postprandial glucose (MD −12.99 mg/dL, 95% CI −27.74 to 1.76; I2 = 97.93%) and HbA1c (MD −0.46%, 95% CI −0.98 to 0.06; I2 = 99.20%) were not statistically significant. Overall effects on lipid outcomes and laboratory safety markers were also not significant. Subgroup analyses suggested possible variation by participant type, plant part, formulation composition, comparator type, and treatment duration, but these findings were exploratory and accompanied by substantial heterogeneity. Conclusions: Myrtaceae interventions may provide a modest short-term reduction in fasting glycemia among adults with T2DM or prediabetes. However, the clinical significance and generalizability of this finding remain uncertain due to high heterogeneity, short follow-up, absence of low-risk trials, and low to very low certainty of evidence. Current evidence does not support consistent benefits for PPG, HbA1c, lipid outcomes, or long-term safety. These interventions should be considered promising but unproven adjuncts rather than alternatives to standard dysglycemia management.