Berberine vs Metformin: What the One Head-to-Head Trial Found

In type 2 diabetes, berberine and metformin have been compared head to head in one trial: a 2008 Chinese pilot study in 36 newly diagnosed adults, in which three months of berberine at 500 mg three times a day took HbA1c from 9.5% to 7.5% (about 80 to 58 mmol/mol) and fasting glucose from 10.6 to 6.9 mmol/L, an effect the authors called similar to metformin's.¹ It had no placebo group, and it is the trial behind every "natural metformin" headline. If you take metformin, do not stop it, reduce it or swap it for berberine without your diabetes team.

Sources checked on 30 October 2026.

• In type 2 diabetes, one trial, 36 people, no placebo: similar HbA1c falls over three months
• Pooled berberine trials: HbA1c about 0.6 percentage points lower in trials of two weeks to six months, mostly at 900 to 2,400 mg a day, in people with type 2 diabetes
• The one instruction: any change to a diabetes medicine is your GP's or diabetes team's call, never a swap made at home

Why do people compare berberine with metformin?

Because a 2008 trial set them side by side, and the comparison travelled. Berberine is a plant alkaloid from the roots and bark of barberry species and goldenseal; metformin is a synthetic medicine descended from guanidine compounds in goat's rue (French lilac), synthesised in the 1920s and first used for diabetes in 1957.³ So metformin is not "derived from berberine", and combining or swapping them is a prescriber's decision. The Wellgard berberine guide covers the plant, the mechanism and every trial.

What did the one head-to-head trial in diabetes find?

The 2008 study by Yin and colleagues had two parts. In study A, 36 adults with newly diagnosed type 2 diabetes were randomised to berberine 500 mg three times a day or to metformin 500 mg three times a day for three months. In study B, 48 adults poorly controlled on existing treatment added berberine for three months; the paper reports the berberine arm's numbers and calls metformin's effect similar:¹

Two limits sit on those numbers. It was a pilot: 36 people in the comparison, no placebo arm, no blinding described. About a third of participants had transient gut side effects.¹ The pooled picture is more sober: across 37 trials and 3,048 people with type 2 diabetes, berberine lowered HbA1c by about 0.63 percentage points and fasting glucose by about 0.8 mmol/L in trials of two weeks to six months, mostly at 900 to 2,400 mg a day.⁴

Is berberine as good as metformin?

On a three-month HbA1c in one small trial, the fall was similar. Metformin's case rests on outcomes: in the UK Prospective Diabetes Study, overweight people with newly diagnosed type 2 diabetes who took it had fewer diabetes-related complications and deaths over about ten years than those managed with diet alone.² No berberine trial in diabetes has run longer than six months or measured complications. In polycystic ovary syndrome (PCOS, now called polyendocrine metabolic ovarian syndrome or PMOS by the NHS), a pooling of nine trials found no significant difference on insulin resistance, glucose or lipid measures, and adding berberine to metformin was not better than metformin alone.⁵ So "as good as" is true of one marker over one quarter in newly diagnosed people, and unknown for everything else. "Better than" has no evidence.

Can berberine replace metformin, or is it a safer or natural alternative?

Not on the strength of the evidence, and not as a decision made alone. Berberine has pooled evidence for about a 0.6 percentage-point HbA1c fall;⁴ metformin has that and outcome data across decades. "Safer" cuts the other way too. The French food-safety agency's 2019 opinion advised people with diabetes not to take berberine supplements, because of its drug-like effects from 400 mg a day and its interactions with their medicines.¹⁴ And "natural" describes where a molecule came from, not how it behaves: berberine inhibits liver enzymes that clear common medicines, as set out below.⁶ If metformin's side effects are the problem, the NHS metformin page describes them and your GP or diabetes nurse decides what to do.

Can you take berberine as well as metformin?

Many people in the trials did: the pooled evidence covers berberine alone and added to standard treatment.^{1, 4} In a 2025 crossover study, adults with type 2 diabetes stabilised on metformin took goldenseal, a berberine-containing plant: metformin exposure did not change meaningfully, though it fell by about a fifth at low metformin doses.⁷ The bigger point is additive glucose lowering: added to existing treatment in a 48-person pilot, berberine took HbA1c from 8.1% to 7.3%.¹ Metformin alone rarely causes a hypo, but your readings will move, and a team adjusting your treatment on those readings needs to know why. What medicines interact with berberine covers the rest.

Berberine with gliclazide, glimepiride or insulin: the hypo question

This is where the forum reports of lows and dizziness come from. Gliclazide and glimepiride make the pancreas release insulin whether or not glucose is high, and injected insulin acts regardless; both can cause hypoglycaemia alone, as the NHS gliclazide page describes. Berberine's trials did not show more hypoglycaemia than control (pooled risk ratio 0.48, not statistically significant), but they tested it alone or added to oral diabetes tablets, not to insulin.⁴ If you take any medicine that can cause a hypo, speak to the team first and know the symptoms from the NHS hypoglycaemia page.

Berberine or metformin for weight loss?

Neither is a weight-loss medicine; in PCOS trials comparing them, BMI did not differ and the waist was 2.74 cm smaller on berberine.¹³ Berberine's pooled trials, in adults mostly with metabolic conditions, reduced body weight by about 0.9 kg across 23 trials, or about 2 kg in the most favourable pooling of 12.^{8, 9} Metformin in the Diabetes Prevention Program reduced body weight by about 2% over two years against no change on placebo, held for ten years in people who kept taking it.¹⁰ Does berberine work for weight loss sets the figures beside the injectable medicines.

Before you take berberine with metformin

Berberine displaces bilirubin from its carrier protein, which is why it is avoided in pregnancy, breastfeeding and infancy: in a jaundiced newborn the freed bilirubin can damage the brain.¹¹ The French food-safety agency's 2019 opinion also advises children, adolescents and people with diabetes or liver or heart conditions not to take berberine supplements.¹⁴ In transplant patients it raised blood levels of ciclosporin by about 29%, and two weeks at 900 mg a day reduced the activity of the CYP3A4, CYP2D6 and CYP2C9 enzymes that clear many antidepressants, anticoagulants, statins and blood-pressure medicines, so anyone on regular medication asks a pharmacist first.^{6, 12} Berberine side effects and who should avoid it has the full list.

What we don't know

Whether berberine matches metformin beyond one marker in newly diagnosed adults: the one comparison had no placebo arm, and no berberine trial has measured heart attacks, strokes, kidney or eye disease.^{1, 4} Whether adding it to insulin or gliclazide raises hypo risk, since the pooled trials tested it alone or with oral tablets.⁴

Frequently asked questions

What herb acts like metformin, or is equal to it?

Berberine is the one with direct comparisons: in diabetes a 36-person pilot with no placebo, and in PCOS nine pooled trials with no significant difference.^{1, 5}

Is there a tablet you can take instead of metformin? What to ask your diabetes team

A prescribing question: several classes of type 2 diabetes medicine exist, and your GP or diabetes team chooses between them on your kidneys, weight, heart and what you could not tolerate. No supplement is on that list.

Is berberine a safer alternative to metformin?

The course agreed with your diabetes team. The French food-safety agency advises people with diabetes to avoid berberine supplements.¹⁴

Can I take berberine with levothyroxine instead of metformin?

Not instead of metformin. No study has tested berberine with levothyroxine; take them hours apart as a precaution and tell your GP.

Sources

1. Yin J, Xing H, Ye J. Efficacy of berberine in patients with type 2 diabetes mellitus. Metabolism, 2008. Pilot trials, 36 and 48 adults with type 2 diabetes, 3 months; hospital and US public funding. PubMed 18442638.
2. UK Prospective Diabetes Study Group. Effect of intensive blood-glucose control with metformin on complications in overweight patients with type 2 diabetes (UKPDS 34). Lancet, 1998. Randomised trial, 753 overweight adults with newly diagnosed type 2 diabetes, median 10.7 years; funding not stated on PubMed. PubMed 9742977.
3. Bailey CJ. Metformin: historical overview. Diabetologia, 2017. Narrative review. PubMed 28776081.
4. Xie W, et al. Glucose-lowering effect of berberine on type 2 diabetes. Frontiers in Pharmacology, 2022. Meta-analysis, 37 randomised trials, 3,048 adults with type 2 diabetes; no conflicts declared. PubMed 36467075.
5. Li MF, et al. Evidence-Based Complementary and Alternative Medicine, 2018. Meta-analysis, 9 randomised trials in PCOS with insulin resistance; funding not stated on PubMed. PubMed 30538756.
6. Guo Y, et al. Repeated administration of berberine inhibits cytochromes P450 in humans. European Journal of Clinical Pharmacology, 2012. Crossover study in healthy men, 2 weeks; no conflicts declared. PubMed 21870106.
7. Nguyen JT, et al. Clinical and Translational Science, 2025. Crossover study in adults with type 2 diabetes on metformin; no conflicts declared. PubMed 39943692.
8. Elahi Vahed I, et al. The effect of berberine on obesity indices. International Journal of Obesity, 2026. Meta-analysis, 23 randomised trials in adults; no conflicts declared. PubMed 41310257.
9. Asbaghi O, et al. The effect of berberine supplementation on obesity parameters, inflammation and liver function enzymes. Clinical Nutrition ESPEN, 2020. Meta-analysis, 12 randomised trials; no conflicts declared. PubMed 32690176.
10. Diabetes Prevention Program Research Group. Long-term safety, tolerability, and weight loss associated with metformin in the Diabetes Prevention Program Outcomes Study. Diabetes Care, 2012. Randomised trial with 7 to 8 years of open-label follow-up in adults at high risk of diabetes; funding not stated on PubMed. PubMed 22442396.
11. Chan E. Displacement of bilirubin from albumin by berberine. Biology of the Neonate, 1993. Laboratory and rat study. PubMed 8513024.
12. Wu X, et al. European Journal of Clinical Pharmacology, 2005. Controlled trial, 104 kidney-transplant recipients, 3 months; funding not stated on PubMed. PubMed 16133554.
13. Xie L, et al. Evidence-Based Complementary and Alternative Medicine, 2019. Meta-analysis, 12 randomised trials in PCOS; no conflicts declared. PubMed 31915452.
14. ANSES. Opinion on the safety of berberine-containing plants in food supplements, saisine 2018-SA-0095. Agency opinion, in French, 1 August 2019. anses.fr.

Spotted something out of date? Email support@wellgard.co.uk with the page address and the sentence.

This article is general information, not medical advice. Never stop, reduce or replace metformin or any other prescribed medicine on the strength of a supplement; if you take a diabetes medicine and want to try berberine, speak to your GP or diabetes team first.