Prevalence, Patterns, and Glycaemic Impact of Herb–Metformin Co-administration in Patients with Type 2 Diabetes Mellitus: A Prospective Observational Study

metabolic disorder characterized by insulin resistance and progressive β-cell dysfunction, leading to sustained hyperglycaemia and long-term complications involving the cardiovascular, renal, neurological, and ocular systems. The global prevalence of diabetes continues to rise at an alarming rate, with the burden disproportionately affecting low- and middle-income countries. India, in particular, faces a rapidly escalating diabetes epidemic due to urbanization, sedentary lifestyles, dietary transitions, and genetic predisposition.

Metformin remains the cornerstone of pharmacological therapy for T2DM owing to its efficacy, cardiovascular benefits, weight neutrality, and low cost. Despite its widespread use, many patients fail to achieve optimal glycaemic targets. Factors such as disease progression, adverse effects, polypharmacy, and poor adherence contribute to suboptimal outcomes. Consequently, patients increasingly turn to complementary and alternative medicine (CAM), especially herbal remedies, either as adjuncts or substitutes for conventional therapy.

Herbal medicines are deeply rooted in traditional medical systems such as Ayurveda, Unani, Siddha, and folk medicine. Antidiabetic herbs like bitter gourd, fenugreek, gymnema, cinnamon, aloe vera, and jamun are widely consumed in various forms. While these herbs exhibit glucose-lowering properties, their concurrent use with metformin raises concerns regarding herb–drug interactions, altered therapeutic response, and safety.

Despite widespread use, herbal medicine consumption is frequently underreported, and clinicians often fail to inquire about CAM use. This lack of communication increases the risk of unrecognized interactions. Therefore, real-world prospective studies are essential to document herbal usage patterns and their clinical implications.

Table 1. Demographic Characteristics of the Study Population (n = 400)

Table 2. Prevalence of Herbal Medicine Use

Table 3. Commonly Used Antidiabetic Herbs among Herbal Users (n = 162)

Table 4. Comparison of Glycaemic Parameters Between Groups

Table 5. Disclosure of Herbal Medicine Use (n = 162)

A key finding of this study is that approximately 40% of patients receiving metformin-based therapy reported concurrent use of herbal medicines. This prevalence is consistent with previous reports from India and other Asian countries, where herbal medicine use among patients with chronic diseases ranges from 30% to 70%. The high prevalence observed in the present study reflects the deep-rooted cultural acceptance of traditional remedies, easy accessibility of herbal products, perceived safety of “natural” therapies, and the chronic nature of diabetes that often prompts patients to seek adjunctive treatment options.

The observed prevalence underscores that herbal medicine use is not a marginal practice but rather an integral component of diabetes self-management for a significant proportion of patients. Importantly, because this was a prospective study with systematic documentation, the findings likely represent a more accurate estimate than retrospective or survey-based studies, which are often affected by recall bias and underreporting.

The study identified Momordica charantia (bitter gourd), Trigonella foenum-graecum (fenugreek), Gymnema sylvestre, cinnamon, and aloe vera as the most commonly used antidiabetic herbs. These findings align closely with ethnopharmacological data from India and Southeast Asia, where these herbs are traditionally consumed as dietary components or medicinal preparations.

The predominance of bitter gourd and fenugreek use is particularly noteworthy. Both herbs are commonly incorporated into daily diets and are frequently recommended by family members, traditional healers, and informal health networks. Their widespread use may reflect not only perceived antidiabetic efficacy but also their affordability and availability in raw or minimally processed forms.

Importantly, many patients reported using more than one herbal product concurrently, often without standardized dosing or clear knowledge of active constituents. This polyherbal exposure increases the complexity of potential interactions and introduces variability in clinical outcomes, emphasizing the need for cautious interpretation of glycaemic benefits.

One of the most clinically relevant findings of this study is the observation that patients using herbal medicines alongside metformin demonstrated statistically significant reductions in fasting plasma glucose (FPG), post-prandial glucose (PPG), and HbA1c compared to non-users. These findings suggest that herbal products may exert additive or synergistic glucose-lowering effects when combined with metformin.

The reduction in HbA1c observed among herbal users, although modest, is clinically meaningful. Even small reductions in HbA1c have been shown to reduce the risk of microvascular complications in T2DM. The observed improvements in glycaemic parameters may be explained by overlapping pharmacodynamic mechanisms between metformin and commonly used antidiabetic herbs.

Several herbs identified in this study have been shown to enhance insulin sensitivity, suppress hepatic gluconeogenesis, delay carbohydrate absorption, or stimulate insulin secretion. These mechanisms complement metformin’s primary action of reducing hepatic glucose production and improving peripheral insulin sensitivity. The convergence of these pathways likely contributes to improved glycaemic control in herbal users.

However, it is important to emphasize that the observational nature of this study precludes definitive causal inference. Improved glycaemic control among herbal users may also reflect confounding factors such as greater health consciousness, dietary modification, or increased adherence to therapy. Nevertheless, the consistent and statistically significant differences observed across multiple glycaemic parameters strengthen the plausibility of a true biological effect.

Clinical Significance of Improved Glycaemic Control

While improved glycaemic outcomes among herbal users may initially appear beneficial, they must be interpreted within a broader clinical context. Metformin monotherapy is associated with a low risk of hypoglycaemia; however, when combined with agents—herbal or pharmacological—that possess intrinsic glucose-lowering activity, the risk profile may change.

The present study demonstrates improved glycaemic indices without excessive reduction in mean glucose levels at the population level. However, subgroup analysis revealed increased variability among herbal users, suggesting that certain individuals may be more susceptible to excessive glucose lowering. This interindividual variability highlights the need for individualized assessment and monitoring, particularly in elderly patients and those with long-standing diabetes.

Herbal medicine use is common and clinically relevant among T2DM patients receiving metformin. Incorporating routine herbal use assessment into diabetes care is essential for optimizing glycaemic control.

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