I read how much reduction of HbA1C from Metformin from some journal on the net. The data was similar to this one ...
http://www.jwatch.org/jw201204030000003/2012/04/03/how-much-does-metformin-lower-hba1c-level
- In comparisons between metformin monotherapy and placebo (or no drug treatment), metformin reduced mean HbA1c level by 1.1%.
- In comparisons involving metformin plus insulin versus insulin alone, addition of metformin reduced mean HbA1c level by 0.8% in patients with type 2 diabetes. In patients with type 1 diabetes receiving insulin, add-on metformin therapy had no HbA1c-lowering effect.
- In comparisons between low-dose and high-dose metformin (usually 1000 vs. 2000 mg daily), HbA1c level was 0.3% lower with high-dose therapy.
See this diagram to see what a 1% reduction looks like e.g. 86 to 75 mmol/mol.