Endocrinology · Medical Literature
Efficacy of Gegen Qinlian decoction plus metformin for type 2 diabetes mellitus: a systematic review and meta-analysis of randomized controlled trials.
Abstract
Gegen Qinlian Decoction (GQD) is frequently used as an adjunctive therapy to metformin for type 2 diabetes mellitus (T2DM), but the certainty and consistency of the supporting clinical evidence remain unclear. We searched CNKI, Wanfang Data, PubMed, EMBASE, Web of Science, and the Cochrane Central Register of Controlled Trials from database inception to January 31, 2026. Randomized controlled trials comparing GQD plus metformin with metformin alone in adults with T2DM were included. The primary outcome was glycated hemoglobin (HbA1c), and secondary outcomes were fasting plasma glucose (FPG) and 2-hour postprandial glucose (2hPG). Risk of bias was assessed using the Cochrane RoB 2 tool, and the certainty of evidence was evaluated using the GRADE framework. Random-effects meta-analyses were performed, with the primary analyses based on change-from-baseline values. Eight randomized controlled trials involving 725 participants were included. In the primary change-score analysis, GQD plus metformin did not show a statistically significant reduction in HbA1c compared with metformin alone (mean difference [MD] = -1.92, 95% confidence interval [CI]: -4.43 to 0.59, P = 0.13). Statistically significant reductions were observed for 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). However, substantial heterogeneity was present across analyses (I² = 85%-100%), and the certainty of evidence was rated as very low because of risk of bias, inconsistency, and imprecision. Post-treatment sensitivity analyses using all eight trials showed statistically significant reductions in HbA1c, FPG, and 2hPG, but these analyses were also affected by substantial heterogeneity and high risk of bias across the included trials. Current evidence is insufficient to confirm a reliable clinical benefit of GQD as an adjunct to metformin for T2DM. Although reductions in FPG and 2hPG were observed, these findings should be interpreted as exploratory because of substantial heterogeneity, methodological limitations, and very low certainty of evidence. Larger, prospectively registered, well-designed, and adequately blinded randomized trials are needed.
Clinical relevance
In adults with type 2 diabetes mellitus already receiving metformin, does adjunctive Gegen Qinlian Decoction (GQD) produce a statistically and clinically significant reduction in HbA1c, fasting plasma glucose, or 2-hour postprandial glucose compared with metformin alone? __SNAPSHOT__ {"studyDesign":"Systematic review with random-effects meta-analysis of randomized controlled trials (PRISMA 2020-compliant)","setting":"All included studies conducted in China; Chinese- and English-language databases searched (CNKI, Wanfang Data, PubMed, EMBASE, Web of Science, Cochrane CENTRAL) from inception to January 31, 2026","sampleSize":"n = 725 across 8 RCTs; individual trial sizes ranged from 40 to 169 participants","population":"Adults with established type 2 diabetes mellitus; all trials were conducted in China. Baseline characteristics (mean age, HbA1c, diabetes duration, BMI) varied across trials and are not uniformly reported in the abstract.","intervention":"GQD (Gegen Qinlian Decoction) plus metformin — GQD formulation, dose, and duration varied across trials (treatment duration ranged from 2 weeks to 6 months)","comparator":"Metformin alone (studies with any additional hypoglycemic agent in either arm were excluded to isolate GQD's adjunctive effect)","primaryOutcome":"Change from baseline in glycated hemoglobin (HbA1c); secondary outcomes were change from baseline in fasting plasma glucose (FPG) and 2-hour postprandial glucose (2hPG)","followUp":"Ranged from 2 weeks to 6 months across included trials; not standardized","fundingSource":"Not reported"}
Key findings
Eight RCTs enrolling 725 participants were included. In the primary pre-specified change-from-baseline analysis, GQD plus metformin did not produce a statistically significant reduction in HbA1c versus metformin alone (MD = −1.92 percentage points, 95% CI: −4.43 to +0.59; P = 0.13). The confidence interval crosses zero and is exceptionally wide, indicating substantial imprecision. For secondary outcomes using change-from-baseline data, statistically significant reductions were observed for FPG (MD = −1.08 mmol/L, 95% CI: −1.71 to −0.44; P = 0.0009) and 2hPG (MD = −1.73 mmol/L, 95% CI: −3.05 to −0.42; P = 0.010). However, extreme statistical heterogeneity was present across all analyses (I² = 85%–100%), severely undermining the interpretability and reliability of all pooled estimates. A sensitivity analysis using post-treatment (endpoint) values across all 8 trials yielded statistically significant reductions in HbA1c, FPG, and 2hPG, but these analyses were equally affected by substantial heterogeneity and high risk of bias. The GRADE certainty of evidence was rated as very low for all three outcomes. NNT cannot be calculated as no dichotomous clinical outcome data (e.g., proportion achieving HbA1c target) were reported. Adverse event data were not reported in the abstract; safety data are therefore not available for this summary.
Practice implications
This meta-analysis did not establish that GQD added to metformin produces a clinically meaningful or statistically reliable reduction in HbA1c — the primary and most validated glycemic endpoint — in adults with T2DM. Although nominally significant reductions in FPG and 2hPG were observed in the change-from-baseline analyses, these results are rendered highly uncertain by extreme heterogeneity (I² up to 100%), which signals that the pooled estimates may not represent a stable, generalizable treatment effect. The GRADE rating of 'very low certainty' means that the true effect is likely to differ substantially from the estimates reported. Critically, all included trials had high overall risk of bias, driven by insufficient reporting of randomization procedures, absence of blinding or placebo control, and lack of prospectively registered protocols — all known sources of systematic overestimation of treatment effects in TCM trials. The primary HbA1c confidence interval (−4.43 to +0.59 percentage points) is implausibly wide for a meta-analysis of 8 trials and reflects that the change-score analysis was restricted to only 2 trials, an extremely limited evidence base. All included participants were from China, limiting generalizability to other ethnic, dietary, and healthcare contexts. Hard clinical endpoints (cardiovascular events, renal outcomes, mortality) were not assessed. Current evidence does not support a change in clinical practice; clinicians should not routinely recommend GQD as adjunctive therapy to metformin outside of well-designed, adequately powered, placebo-controlled, blinded RCTs. Note: this interpretation is based on the published abstract and the publicly available full-text; details on individual trial-level data, subgroup analyses, and safety reporting require review of the complete article. __LIMITATIONS__ Only 8 RCTs with a total of 725 participants included — severely underpowered evidence base for a meta-analysis of a chronic metabolic condition.,The primary HbA1c change-from-baseline analysis included only 2 trials, making the pooled estimate unreliable and the wide CI (−4.43 to +0.59) clinically uninterpretable.,Extreme statistical heterogeneity (I² = 85%–100%) across all outcomes undermines validity of all pooled estimates and suggests important clinical, methodological, or statistical differences between trials that were not adequately explained.,High overall risk of bias in all included trials, primarily due to inadequate reporting of randomization, lack of blinding, absence of placebo control, and no prospective protocol registration — all of which are known to inflate apparent treatment effects in TCM trials.,All studies were conducted in China; findings may not be generalizable to non-Chinese populations.,Substantial heterogeneity in GQD formulation, dose, and treatment duration (2 weeks to 6 months) across trials precludes meaningful standardization of the intervention.,No hard clinical endpoints (cardiovascular events, hospitalization, mortality, microvascular complications) were assessed — all outcomes are surrogate glycemic markers.,Absence of safety and adverse event data in the abstract prevents assessment of the benefit-risk profile.,Potential for publication bias not fully evaluable with only 8 trials; small-study effects are a recognized concern in TCM literature.,Funding source not reported; potential conflicts of interest cannot be assessed. __BOTTOM_LINE_CATEGORY__ low_certainty __BOTTOM_LINE__ This meta-analysis of 8 small, high-risk-of-bias RCTs did not demonstrate a statistically significant improvement in HbA1c when GQD was added to metformin in adults with T2DM, and the overall certainty of evidence for all outcomes was rated as very low by GRADE. Extreme heterogeneity (I² = 85%–100%) and methodological limitations render the nominally significant reductions in FPG and 2hPG unreliable and clinically uninterpretable. GQD should not be adopted as adjunctive antihyperglycemic therapy outside of adequately powered, double-blind, placebo-controlled trials with prospective registration and hard clinical endpoints.