Berberine matched metformin on blood sugar in 36-patient pilot study

A three-month randomized pilot published in May 2008 in the journal Metabolism reported that the herbal compound berberine lowered blood sugar about as much as metformin in 36 adults who had just been diagnosed with type 2 diabetes ^[1]. The work was led by Jun Yin, Huili Xing and Jianping Ye at Xinhua Hospital in Shanghai ^[1].

In the comparison, called study A, participants took either 500 mg of berberine three times daily or 500 mg of metformin three times daily ^[1]. Average HbA1c, which reflects blood sugar over roughly three months, fell from 9.5% to 7.5% in the berberine group ^[1]. Fasting blood glucose fell from 10.6 mmol/L to 6.9 mmol/L, and blood sugar measured after meals fell from 19.8 mmol/L to 11.1 mmol/L ^[1]. Triglycerides dropped from 1.13 mmol/L to 0.89 mmol/L ^[1]. The paper states that "the hypoglycemic effect of berberine was similar to that of metformin" ^[1].

The paper also describes a second group, study B, in which 48 adults whose type 2 diabetes was not well controlled added 500 mg of berberine three times daily to their existing treatment for three months ^[1]. In that group, HbA1c fell from 8.1% to 7.3%, and fasting insulin and a measure of insulin resistance called HOMA-IR fell by 28.1% and 44.7% ^[1]. Total cholesterol and LDL cholesterol also decreased significantly ^[1]. Ten insulin-treated patients were left out of the HOMA analysis ^[1].

Side effects were mostly digestive. During the trial, 20 patients (34.5%) had transient gastrointestinal effects, and the berberine dose was lowered to 300 mg three times daily when those effects were heavy ^[1]. No functional liver or kidney damage was observed in any patient, the authors report ^[1].

The trial has clear limits. It enrolled 84 people in total, all recruited at one hospital in China, and the authors describe it as a pilot study ^[1]. Berberine is described in the paper as an over-the-counter drug used in China to treat gastrointestinal infections, and as the main active component of the herb Coptis chinensis ^[1]. The study does not report any comparison between berberine and a GLP-1 medication such as semaglutide or tirzepatide, and no such comparison appears in the paper ^[1]. Whether berberine is regulated in the United States as a diabetes treatment is not addressed ^[1].

Why it matters for patients

Berberine is easy to buy in the US as a dietary supplement, and the numbers in this 2008 pilot are the kind that get repeated in marketing. The evidence behind them is thin: 36 people in the head-to-head comparison, a single center, and a three-month window ^[1]. The paper does not show how berberine performs over years, in a diverse population, or alongside modern diabetes drugs, including GLP-1 medications.

The gastrointestinal side effects seen here were common enough that the researchers reduced the dose for some participants, and roughly a third of patients reported them ^[1]. The study was not designed to look for rare or long-term harms, and it does not address whether berberine interacts with prescription diabetes drugs. It also does not say anything about the quality or purity of berberine products sold in the US, which are not reviewed by the Food and Drug Administration the way prescription medicines are.

One practical point for anyone weighing berberine claims against GLP-1 drugs: the two have never been compared in the study described here, and the paper reports nothing about weight, cardiovascular outcomes or the conditions these newer drugs are approved to treat ^[1].

What happens next

The authors describe the work as a pilot and write that "if the efficacy and safety of berberine are confirmed, it can serve as a new class of anti-diabetic medication" ^[1]. No larger or longer confirmation trial is described in the paper, so whether those results were ever replicated in a study of similar design has not been reported ^[1].