Metformin reduces the amount of glucose your liver releases and helps a little with insulin resistance, I believe it also helps with weight loss. If you don't suffer from the unfortunate side effects that some people get it can be a useful drug and help somewhat.
What it can't do is remove any glucose in your blood that is there because of diet, it just doesn't work like that. To lower your glucose levels using medication you need drugs that make you pee the sugar out, or squeeze every last drop of insulin from your already overworked pancreas or insulin injections of course.
By far the easiest way to reduce glucose levels, the most successful and with no side effects is your diet, if you don't eat or drink carbs/sugar they can't find their way into your blood.