Metformin works to reduce A1C levels through several mechanisms:

1. Liver glucose production: Metformin decreases the amount of glucose produced by the liver54.

2. Glucose absorption: It reduces the amount of glucose absorbed from food and drinks in the gut25.

3. Insulin sensitivity: Metformin improves the body's response to its natural insulin, helping combat insulin resistance25.

4. Glycerol conversion: It inhibits the mitochondrial-associated enzyme glycerol phosphate dehydrogenase, which converts glycerol to glucose4.

These combined effects result in lower blood glucose levels, which in turn leads to a reduction in A1C. Metformin typically lowers A1C by about 1% to 2% on average when used as monotherapy13. In some studies, metformin has been shown to lower A1C by up to 1.5%2.

The full glucose-lowering effect of metformin usually takes about 2 months to manifest, although some patients may see improvements in blood glucose levels within the first week of treatment2. Long-term A1C control is typically monitored by healthcare providers every 3 to 6 months to assess the medication's effectiveness3.

Citations:

1. https://www.drugs.com/medical-answers/metformin-lower-a1c-how-3574052/
2. https://www.goodrx.com/metformin/how-long-it-takes-metformin-work
3. https://www.drugs.com/medical-answers/how-long-metformin-take-work-3574615/
4. https://medicine.yale.edu/news-article/how-a-widely-used-diabetes-medication-actually-works/
5. https://www.bannerhealth.com/healthcareblog/better-me/what-you-need-to-know-about-metformin
6. https://hopkinsdiabetesinfo.org/medications-for-type-2-diabetes-metformin/
7. https://pubmed.ncbi.nlm.nih.gov/32936780/
8. https://www.mayoclinic.org/medical-professionals/endocrinology/news/metformin-revisited/mac-20430448

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