The efficacy and safety of herbal medicines for glycaemic control and insulin resistance in individuals with type 2 diabetes: an umbrella review.

Abstract

Aim: The global prevalence of diabetes is increasing rapidly. While glycaemic control remains the cornerstone of type 2 diabetes (T2DM) management, hypoglycaemic medications are associated with side effects. Many individuals with T2DM use herbal medicines despite potential risks. This review aims to comprehensively evaluate the efficacy and safety of herbal medicines for T2DM.

Methods: Four electronic databases were searched from August 2018-August 2023 for umbrella reviews, meta-analyses, and systematic reviews on herbal medicine for T2DM. The primary outcome was glycaemic control assessed by glycated haemoglobin (HbA1c); secondary outcomes included measures of insulin resistance, quality of life and adverse events. Quality assessment was performed using A Measurement Tool to Assess Systematic Reviews Version 2 (AMSTAR 2) and certainty of evidence for the primary outcome was assessed using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) approach.

Results: Eight meta-analyses and two systematic reviews were included. Ginger, turmeric, and Jinlida granules significantly decreased HbA1c compared to placebo (mean differences (MD): -0.467%, -0.486%, -0.283%, respectively) with moderate to high certainty evidence. Berberis vulgaris, Gegen Qinlian decoction and pycnogenol may potentially decrease HbA1c (very low certainty evidence). Ginger, turmeric, cardamom, Berberis vulgaris, Nigella sativa, and various Chinese herbal medicines demonstrated improvements in insulin resistance measures. However, overall confidence in these findings is limited due to the low to very low quality of the included reviews. Few mild adverse effects were reported, but data was incomplete.

Conclusions: Current evidence supports the use of ginger and turmeric for glycaemic control in type 2 diabetes, however, given the high clinical heterogeneity and low quality of the review, our confidence in this finding is somewhat limited. Herbal medicines should be used only as an adjunct to conventional treatment, with shared decision-making between clinicians and patients. Careful monitoring for hypoglycaemia is essential, particularly when herbal medicines are used concurrently with antidiabetic drugs, given a current lack of data on herb-drug interactions. Future research should clarify optimal regimens, safety profiles, and include diverse populations to enhance generalisability.