Berberine's famous match with metformin was one 36-person pilot
It ran once, with no placebo group and no clear blinding. Over three months berberine took the three-month blood-sugar average from 9.5% to 7.5%, metformin from 9.2% to 7.7%.
What the study found
The metformin comparison comes from one pilot with 36 people
The comparison that made berberine famous ran once, in 36 people, with no placebo group and no clear blinding. Over three months berberine took the three-month blood-sugar average from 9.5% to 7.5%; metformin, the standard diabetes drug, went from 9.2% to 7.7% in the same trial.
The caveat · Chance alone could move it that much
Thirty-six people split between two drugs is small enough that an ordinary run of luck moves the number about as much as the drug does. With no placebo group, the fall also contains whatever three months of clinic visits and daily pill-taking do on their own. About a third of patients in the add-on arm had short-lived stomach upset.
What we don't know
Whether berberine lowers blood sugar is not the open question. The head-to-head with metformin everyone quotes came from a pilot with no placebo group, never built to size an effect, and no larger trial has repeated it.