Metformin does not instantly reduce blood sugar levels. The effects are usually noticeable within 48 hours of taking the medication, and the most significant effects take 4–5 days to occur. However, the timing depends on the person's dosage.
Metformin (brand name: Glucophage) will be in your system for 96.8 hours which is approximately 4 days. Metformin has an elimination half-life of approximately 17.6 hours.