Can I Take Berberine with Metformin?

What happens when you take berberine with metformin?

Berberine is a plant alkaloid sold over the counter as a dietary supplement, and a Drugs@FDA search returns no approved drug application listing it as the active ingredient [6]. Metformin is a prescription biguanide approved as an adjunct to diet and exercise for type 2 diabetes [3]. Each lowers glucose on its own [5][3].

No trial has established the safety or added benefit of taking both together [2], and no study of pure berberine's effect on metformin pharmacokinetics was found. The interaction data that do exist come from a berberine-containing botanical extract, described below [1].

The one human study: metformin exposure fell 23%

A 2021 study in Clinical Pharmacology & Therapeutics gave 16 healthy volunteers a probe-drug cocktail that included metformin, alongside a goldenseal extract standardized to berberine. Metformin AUC fell 23% (geometric mean ratio 0.77, 90% CI 0.71 to 0.83), while metformin half-life and renal clearance did not change. The authors said the lower exposure may reflect altered intestinal permeability, transport, or other processes involved in metformin absorption, and noted it could have unfavorable effects on glucose control. The same extract raised midazolam AUC by 43% (ratio 1.43), confirming CYP3A inhibition [1].

Those numbers belong to the extract, which contains other alkaloids besides berberine. Berberine's own exposure also varies between people: in a 2025 study, women had 2.8-fold higher AUC and 3.6-fold higher Cmax than men [8].

Metformin is not metabolized and is excreted unchanged in urine [3]. Separately, berberine at 300 mg three times daily for 14 days inhibited CYP3A4, CYP2D6 and CYP2C9 in 17 healthy men: midazolam AUC rose 40%, the urinary dextromethorphan/dextrorphan ratio rose about ninefold, and the losartan/E-3174 ratio about doubled [9].

Is berberine as good as metformin?

A 36-person pilot published in Metabolism randomized adults with newly diagnosed type 2 diabetes to berberine or metformin, both at 0.5 g three times daily, for 3 months. Glucose lowering was similar between groups; in the berberine arm, HbA1c fell from 9.5% to 7.5% and fasting glucose from 10.6 to 6.9 mmol/L [2]. That is one 3-month pilot, and larger head-to-head trials with long-term outcomes are lacking [2].

Do the glucose-lowering effects add up?

The combination can add glucose lowering and add GI side effects [2]. Berberine's own effect is modest: across 37 randomized trials in 3,048 patients with type 2 diabetes, HbA1c fell 0.63 percentage points (95% CI -0.72 to -0.53) and fasting glucose fell 0.82 mmol/L, with a larger effect when baseline glucose and HbA1c were higher. Total adverse events and hypoglycemia did not increase [5].

Metformin's label raises the hypoglycemia concern mainly for insulin and insulin secretagogues: when metformin is combined with insulin or a sulfonylurea, the risk of low blood sugar goes up and lower doses of those drugs may be needed [3].

Will the gastrointestinal side effects stack?

Diarrhea and nausea are the most likely overlap. In the metformin label's US trial of immediate-release tablets up to 2,550 mg daily (141 patients) versus placebo (145), diarrhea occurred in 53% versus 12%, nausea or vomiting in 26% versus 8%, and flatulence in 12% versus 6%; diarrhea led 6% of metformin patients to stop [3].

Berberine trials report GI effects too. Across 18 placebo-controlled lipid trials (1,788 participants, 900-1,500 mg daily for 4 to 24 weeks), the 12 trials that reported GI adverse events showed 2-23% with berberine versus 2-15% with placebo; these tended to be more frequent with berberine, and no serious adverse events were reported [4]. In the two Yin diabetes studies, 20 patients (34.5%) had transient GI effects [2].

What does the metformin label say to watch for?

• Kidney function. The label says to check eGFR before starting and at least yearly. Metformin is contraindicated below an eGFR of 30 mL/min/1.73 m2, starting is not recommended at 30 to 45, and if eGFR later falls below 45 the benefit and risk of continuing should be reassessed [3].
• Lactic acidosis. A boxed warning covers it, with risk factors including renal impairment, age 65 or older, contrast imaging, surgery, hypoxic states such as acute heart failure, excessive alcohol intake and hepatic impairment [3]. The label says drugs that interfere with the renal tubular transport systems that clear metformin, such as ranolazine, vandetanib, dolutegravir and cimetidine, can raise metformin exposure and may increase lactic acidosis risk [3].
• Vitamin B12. Subnormal B12 occurred in about 7% of patients in 29-week trials, and the label says to measure B12 every 2 to 3 years [3].

What is known about berberine's longer-term safety?

Controlled berberine trials run 12 weeks or less, and meta-analyses cover 4 to 24 weeks; long-term safety is unknown [7][4]. Most human trials are also small and done in China or Hong Kong, and a 2026 integrity-based reappraisal rated all four eligible berberine trials in polycystic ovary syndrome (n=452) at high risk of compromised integrity [11].

A 2026 toxicology review of Berberis alkaloids reports liver, kidney, cardiovascular and immune toxicity and effects on embryonic development under specific doses and conditions, modulated by dose, genetics, pregnancy, liver and kidney function, and CYP450/P-glycoprotein interactions [7]. In laboratory work, berberine displaced bilirubin from albumin about tenfold more than phenylbutazone on a molar basis and raised unbound bilirubin in rats; those authors advised avoiding berberine-rich products in jaundiced newborns and pregnant women [10]. Safety in pregnancy and breastfeeding is not established.

Bottom line

Both drugs lower glucose and both can cause diarrhea and nausea [2][3]. Berberine is not an FDA-approved drug and its long-term safety is unknown [6][7]. The metformin label says to check kidney function and names the drugs that raise metformin levels [3].

Metformin is a prescription treatment labeled to improve blood glucose control in type 2 diabetes.