Metformin's primary clinical effect in poorly controlled diabetes is the inhibition of gluconeogenesis.

“metformin lowers glucose in patients with poorly controlled diabetes mostly through inhibition of gluconeogenesis i think most clinical physiologists would agree with that and so we've done studies quantifying gluconeogenesis both by nmr heavy water multiple methods same individuals and that's its major effect not through inhibition of glycogenolysis not through gut biome it's gluconeogenesis”