Your genes may be signaling how well you respond to metformin. If you have the right genetic makeup, metformin may lower your A1C score to a healthy level. A change or variation in gene that tells the body how to create a small structure with cells call an organic cation transporter 1 (OCT1) contributes to metformin's effectiveness. (A simplified explanation of an organic cation transporter is a chemical that helps certain atoms to enter a cell.)
In a recent clinical trial, people who had genetic variations that reduced the function of OCT1 also had less success at lowering blood glucose with metformin. This study does not suggest that patients considering metformin take a genetic test. Perhaps that will occur someday. For now, if metformin is not helping you control your blood sugar, the best strategy may be to combine another medication with it, or switch to a different mediction altogether. Your doctor will be your best resource for making this decision.
The Wall Street Journal published an article about genes and medications back in August, that is more general than diabetes. It highlights an individual very sensitive to the blood thinner warafin. It reinforces the fact that there is always a risk with medications, and people can have strange unforseen reactions. Medicine is amazing in most cases, but it is good to realize that problems can occur.