Objective:

To evaluate the efficacy and certainty of evidence for GQD plus metformin compared with metformin alone in adults with T2DM.

Approach:

• Study Design: Systematic review and meta-analysis of randomized controlled trials.
• Data Sources: Search conducted across CNKI, Wanfang Data, PubMed, EMBASE, Web of Science, and Cochrane Central Register of Controlled Trials.
• Eligibility Criteria: Included adults with T2DM receiving GQD plus metformin versus metformin alone; excluded studies with additional hypoglycemic drugs.
• Outcomes: Primary outcome was HbA1c; secondary outcomes were fasting plasma glucose (FPG) and 2-hour postprandial glucose (2hPG).

Key Findings:

• Eight randomized controlled trials with 725 participants were included.
• No statistically significant reduction in HbA1c with GQD plus metformin compared to metformin alone (MD = -1.92, 95% CI: -4.43 to 0.59, P = 0.13).
• Statistically significant reductions in FPG (MD = -1.08, 95% CI: -1.71 to -0.44, P = 0.0009) and 2hPG (MD = -1.73, 95% CI: -3.05 to -0.42, P = 0.010) were observed.
• Substantial heterogeneity was present across analyses (I² = 85%–100%).
• The certainty of evidence was rated as very low due to risk of bias, inconsistency, and imprecision.

Interpretation:

Current evidence is insufficient to confirm a reliable clinical benefit of GQD as an adjunct to metformin for T2DM.

Limitations:

• Substantial heterogeneity in trial results.
• High risk of bias across included trials.
• Very low certainty of evidence due to methodological limitations, including small sample sizes and limited reporting.

Conclusion:

Larger, well-designed, and adequately blinded randomized trials are needed to clarify the efficacy of GQD combined with metformin.