Protocol
Berberine 1.0 to 1.2 g/day (with meals)
Placebo-controlled trials lower HbA1c A blood test that reflects average blood sugar over the previous two to three months. and LDL Low-density lipoprotein cholesterol, the cholesterol fraction most closely tied to plaque in the arteries. cholesterol in type 2 diabetes: in Zhang 2008 (PMID PubMed ID: the permanent number the US National Library of Medicine gives a published paper. Each one links to that paper's record on PubMed. 18397984) HbA1c fell from 7.5 to 6.6 percent and LDL from 3.23 to 2.55 mmol/L within the berberine arm, with smaller differences against placebo An inactive substitute made to look like the real treatment, so participants cannot tell which one they received.; PREMOTE (409 patients, 20 centers) found HbA1c 0.4 points lower than placebo.
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How this letter has changedLatest: October 2026 · Corrected.
Placebo-controlled replication The same finding reproduced by a separate research group. A result seen once can be chance or bias; a replicated one is harder to explain away. is on the record: Zhang et al. (J Clin Endocrinol Metab, 2008; PMID 18397984), PREMOTE (PMID 33024120), Ming 2021 (PMID 34365978) and Zhao 2023 (PMID 37598753), so the flag applied only to the metformin comparison, which the reading already confines to the 36-person pilot (Yin et al., Metabolism, 2008; PMID 18442638). Flag removed. The written B attaches to the dose the trials used, and those trials gave 1.0 to 1.2 g/day where the name said 1.5 g/day, so the name now reads Berberine 1.0 to 1.2 g/day (with meals). Applied the written grade definition under the editor's standing instruction of October 2026 (Arnold Sandlow, D.C.).PMID 18397984 PMID 18442638 PMID 33024120 PMID 34365978 PMID 37598753
The description gave Zhang 2008 (PMID 18397984) within-arm changes as differences versus placebo, called the single 36-person Yin 2008 pilot (PMID 18442638) a metformin equivalence, and said Zhang's primary outcome was HbA1c when it was plasma glucose and lipids; all corrected. Xie 2022 (PMID 36467075) is described as pooling berberine with and without other drugs. The placebo-controlled replication is now cited: PREMOTE (PMID 33024120), Ming 2021 (PMID 34365978), Zhao 2023 (PMID 37598753). The 'mandatory interaction check' wording is replaced by the interaction evidence itself, Guo 2012 (PMID 21870106). The record now says the B is drawn from 1.0 to 1.2 g/day trials and that 1.5 g/day matches only the pilot. Letter unchanged.PMID 18397984 PMID 18442638 PMID 36467075 PMID 33024120 PMID 34365978 PMID 37598753 PMID 21870106
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Berberine is a plant compound sold as a supplement. In people with type 2 diabetes, 1.0 to 1.2 grams a day lowered long-term blood sugar and LDL cholesterol more than a dummy pill. The largest study, of 409 patients, found a modest drop. The claim that it works as well as metformin comes from one small study of 36 people. It has not been tested in people without diabetes. Berberine slows liver enzymes that clear many drugs, and stomach side effects are more common than with a dummy pill.
Placebo-controlled trials lower HbA1c and LDL cholesterol in type 2 diabetes: in Zhang 2008 (PMID 18397984) HbA1c fell from 7.5 to 6.6 percent and LDL from 3.23 to 2.55 mmol/L within the berberine arm, with smaller differences against placebo; PREMOTE (409 patients, 20 centers) found HbA1c 0.4 points lower than placebo. 'Comparable to metformin' rests on one 36-person pilot with no stated primary endpoint The one outcome a trial names in advance as its main test. Results on other outcomes carry less weight.. The protocol is named for the 1.0 to 1.2 g/day the placebo-controlled trials used; the 1.5 g/day of the earlier name matched only the pilot. Berberine inhibits CYP2D6, CYP2C9 and CYP3A4 in humans, and gastrointestinal side effects are more common than on placebo.
Why this gradeThe reasoning, and what the grade does not cover.
Grade B on HbA1c and LDL cholesterol in type 2 diabetes. In a placebo-controlled trial of 116 patients at 1.0 g/day, HbA1c fell from 7.5 to 6.6 percent and LDL from 3.23 to 2.55 mmol/L within the berberine arm, each significantly different from placebo (Zhang et al., 2008; PMID 18397984). PREMOTE, 409 patients at 20 centers, found HbA1c 0.4 points lower than placebo (PMID 33024120).
WHY NOT Aboth endpoints The outcome a trial measures to decide whether the treatment worked, such as heart attacks, blood pressure or a symptom score. are surrogates.
WHAT THIS GRADE DOES NOT COVER1.5 g/day, the dose of this protocol's earlier name, which matches only a 36-person pilot (Yin et al., 2008; PMID 18442638) and was replaced in October 2026 by the dose the placebo-controlled trials used; the claim that berberine is comparable to metformin, which rests on that pilot; and people without diabetes. Berberine inhibits CYP2D6, CYP2C9 and CYP3A4 in humans (PMID 21870106).
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The evidence, in fullSeven papers, each linked to its PubMed record.
Yin et al. (Metabolism, 2008; PMID 18442638): pilot, study A randomized 36 newly diagnosed patients to berberine or metformin 0.5 g three times daily for 3 months with similar HbA1c falls (9.5 to 7.5 percent on berberine); study B had no control arm; no primary endpoint is stated; the metformin comparison has not been replicated; funded by the NIH. Zhang et al. (J Clin Endocrinol Metab, 2008; PMID 18397984): 116 patients, berberine 1.0 g/day versus placebo for 3 months; primary outcomes plasma glucose and serum lipids; HbA1c 7.5 to 6.6 percent and LDL 3.23 to 2.55 mmol/L within the berberine arm, each significantly different from placebo; clamp-measured glucose disposal did not differ from placebo (P = 0.063). Replication: PREMOTE (Zhang et al., Nat Commun, 2020; PMID 33024120), 409 newly diagnosed patients, 20 centers, HbA1c the primary outcome, berberine alone 0.99 points versus 0.59 on placebo (P < 0.001), more gastrointestinal side effects; Ming et al. (Genome Med, 2021; PMID 34365978), 300 adults with new hyperglycemia, 16 weeks, fasting glucose 0.50 mmol/L lower than placebo, drugs supplied free by two pharmaceutical companies. Pooled: Zhao et al. (J Nutr, 2023; PMID 37598753), 20 placebo-controlled trials, HbA1c 4.5 mmol/mol (about 0.4 percent) lower, fasting glucose 0.52 mmol/L lower; Xie et al. (Front Pharmacol, 2022; PMID 36467075), 37 trials, HbA1c 0.63 points lower, but the pooled set mixes berberine alone with berberine added to other glucose-lowering drugs. Interactions: Guo et al. (Eur J Clin Pharmacol, 2012; PMID 21870106), berberine 300 mg three times daily for 2 weeks inhibited CYP2D6, CYP2C9 and CYP3A4 in healthy men. Grade B: replicated placebo-controlled trials on glycemic and lipid surrogates.
Fasting glucose and HbA1c at baseline and 12 weeks: the meta-analysis A study that pools the numbers from several trials into one combined estimate. of 27 RCTs Randomized controlled trial: people are assigned to the treatment or a comparison by chance, so the groups differ only in what they received. It is the design that can show cause and effect. showed effects comparable to metformin at this dose. Fasting insulin and HOMA-IR at 12 weeks. Drug interactions before starting: berberine inhibits CYP3A4 and P-glycoprotein and can significantly elevate levels of cyclosporine, digoxin, and some statins.
Evidence notes: randomized trial, meta-analysis
Endpoint graded: HbA1c and LDL cholesterol in type 2 diabetes (surrogate)
Last reviewed: July 2026
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berberine[tiab] AND (diabetes[tiab] OR glyc*[tiab] OR HbA1c[tiab]) AND (randomized controlled trial[pt] OR meta-analysis[pt]) AND humans[mesh]Grades move when new trials publish. A free monthly email lists every grade EBL moved, with the reason and the trial behind it: the sign-up is on the Evidence Log →