Short answer: Metformin is an FDA-approved diabetes drug; berberine is a plant supplement with no FDA approval.12 In one small 3-month trial of 36 adults with new type 2 diabetes, berberine and metformin (each 0.5 g three times a day) lowered blood sugar by a similar amount; HbA1c on berberine fell from 9.5% to 7.5%.3 No large head-to-head trial exists.
| Berberine | Metformin | |
|---|---|---|
| What it is | Plant compound sold as a dietary supplement2 | Biguanide prescription drug1 |
| FDA approved for | Nothing; supplements are not approved before sale2 | Blood sugar control in type 2 diabetes, adults and children 10 and older1 |
| Amounts used | Pilot trial: 0.5 g three times a day3 | Label: start 500 mg twice a day or 850 mg once a day with meals; up to 2,550 mg a day1 |
| Half-life | About 30.6 hours after one 300 mg dose, with wide variation4 | About 6.2 hours in plasma1 |
| Main stomach side effects | Passing stomach upset in 34.5% across the pilot trials3 | Diarrhea 53% vs 12% on placebo; nausea or vomiting 26% vs 8%1 |
| Boxed warning | None (not a labeled drug) | Lactic acidosis1 |
| Kidney limit | Not set by any label | Not used when eGFR is below 301 |
| Interactions | Reported to block CYP3A4, CYP2D6 and CYP2C9 liver enzymes5 | Low blood sugar risk is higher with insulin or insulin secretagogues1 |
In 2008, researchers in Shanghai randomized 36 adults with newly diagnosed type 2 diabetes to berberine or metformin, each 0.5 g three times a day, for 3 months. They reported that berberine lowered blood sugar about as much as metformin. In the berberine group, HbA1c fell from 9.5% to 7.5% and fasting glucose from 10.6 to 6.9 mmol/L.3
This was a small pilot study. It was not a large or long trial, and it was not designed to show the two are equal. A second part of the same paper added berberine for 48 adults with poorly controlled diabetes and found HbA1c fell from 8.1% to 7.3%, but that part had no comparison group.3 These are study protocols, not personalized advice; confirm any dosing with your prescriber.
Metformin is made to a set standard, and its label gives tested doses, warnings and kidney limits.1 Berberine is sold as a supplement, so FDA does not review it before sale and the maker is responsible for what is in the bottle.2
Very little berberine reaches the blood: after a single 300 mg dose, the average peak was 0.33 ng/mL.4
If you take both, or take berberine with other medicines, tell your prescriber. More detail: metformin side effects, the metformin dosing schedule, Berberine vs dihydroberberine: is DHB absorbed better?, and the Berberine and Metformin guides.