Why people call it "nature's metformin"
Berberine is a bitter yellow compound found in plants such as barberry, goldenseal and Oregon grape. Plants containing berberine have been used in traditional Chinese and Ayurvedic medicine for thousands of years (NCCIH). Online, berberine is often sold as "nature's metformin", a natural swap for metformin (the most commonly prescribed diabetes medicine, according to the NCCIH).
It does lower blood sugar in some trials. But is it a replacement? No.
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What the trials found
In a small 2008 pilot from China, 36 adults with newly diagnosed type 2 diabetes were randomly assigned to berberine or metformin, 500 mg three times a day, for 3 months. Blood sugar fell by a similar amount in both groups; in the berberine group, HbA1c (a 3-month average of blood sugar) dropped from 9.5% to 7.5% (Yin et al., 2008).
A larger placebo-controlled trial, PREMOTE, randomly assigned 409 adults in China with newly diagnosed, untreated type 2 diabetes to berberine (0.6 g twice a day before meals), probiotics, both, or placebo for 12 weeks. HbA1c fell by about 1.0 percentage point with berberine alone versus about 0.6 with placebo, a difference of about 0.4 points (Zhang et al., 2020).
Pooling 31 trials (2,683 people with type 2 diabetes), most of which added berberine to diabetes pills, a 2022 meta-analysis found HbA1c about 0.6 points lower than in the comparison groups, and about 0.8 lower when HbA1c started at 9% or higher (Xie et al., 2022).
The catch: most of these trials were small, short and done in China, and reviewers have often rated their quality as low (Dong et al., 2012). The NCCIH says there is only "weak evidence of a possible benefit" for a few supplements, including berberine (NCCIH).
Head to head with metformin
A 2012 review found that, in 7 small trials (448 people, all in China, each lasting 2 to 3 months), berberine did not control blood sugar significantly better than metformin, glipizide or rosiglitazone. The authors rated the quality of the trials as generally low (Dong et al., 2012). "Not better" in small trials is not the same as "proven just as good."
The bigger gap is long-term evidence. In the UK Prospective Diabetes Study, 753 overweight adults with newly diagnosed type 2 diabetes were followed for a median of 10.7 years. Those assigned to metformin had a 32% lower risk of any diabetes-related problem (complications or diabetes-related death) and a 36% lower risk of death from any cause than those treated mainly with diet (UKPDS 34, 1998). The berberine trials above mostly lasted 2 to 3 months and measured blood sugar, not complications or deaths.
| Berberine | Metformin | |
|---|---|---|
| Lowers blood sugar | Yes, in short trials | Yes |
| Key trial length | 12 weeks (PREMOTE) | 10.7 years (UKPDS) |
| Fewer complications | Not shown | Yes (UKPDS) |
| Sold as | Supplement | Prescription drug |
| Common side effects | Stomach upset | Stomach upset |
Side effects and who should skip it
In the 2008 pilot, 20 of the 58 people who took berberine (about a third; most were also taking other diabetes medicines) had temporary digestive side effects such as wind, diarrhea or constipation, mostly in the first month (Yin et al., 2008). In PREMOTE, the berberine groups had more digestive side effects than placebo (Zhang et al., 2020). The NCCIH lists mild-to-moderate nausea, diarrhea, bloating and constipation; metformin's common side effects include feeling sick, diarrhea and tummy pain (NCCIH; NHS).
Skip berberine if you are pregnant or breastfeeding, and never give it to infants: it has been linked to a harmful buildup of bilirubin in babies that can cause brain damage (NCCIH). The trials were in adults.
Berberine may interact with some medicines, and the NCCIH says people who take medicines should talk with their health care provider first. In one NIH-funded study, healthy adults given goldenseal extract (an herb that contains berberine) had about 25% lower metformin levels, enough to potentially weaken blood sugar control; whether pure berberine does the same is not known (NCCIH). In trials, adding berberine to diabetes pills lowered blood sugar further (Dong et al., 2012), so tell your doctor before combining them and keep checking your blood sugar as advised.
If you still want to try it
Talk to your doctor first. Never stop or reduce metformin or any other diabetes medicine on your own. The FDA warns about products sold as a "natural diabetes cure" or a way to "replace your diabetes medicine" (NCCIH).
No official safe upper limit has been set for berberine, and its long-term safety is uncertain (Dong et al., 2012). The diabetes trials above used 1,200 to 1,500 mg a day in divided doses, and some people needed less because of stomach upset (Yin et al., 2008; Zhang et al., 2020). If your doctor agrees, choose berberine capsules with a USP or NSF seal, which means the label matches what's in the bottle (not that the product works), and track readings with a blood glucose meter.
If you're very tired, peeing more than usual, thirsty all the time or losing weight without trying, see a doctor rather than self-treating. Type 2 diabetes is diagnosed with a blood test, and not everyone has symptoms (NHS).
The bottom line
In short, mostly small trials of people with type 2 diabetes, berberine lowered blood sugar, but the evidence is weak and it has not been shown to prevent diabetes complications the way metformin has. It's something to discuss with your doctor, not a swap for your prescription.