That's not due to the metformin, that's because of the kelloggs. Carbs up bloodsugars, and corn flakes are basically all carb. You take metformin with food so the chances of gastro-intestinal side effects are smaller. Not because it does anything about the food you eat. Met lowers your appetite, makes you a little more sensitive to your own insulin, and it tells your liver not to dump too much glucose in the morning. If you want to lower your blood sugars to the normal range, you'll have to look at your diet, or possibly request other medication, if diet is not a viable option for you. https://josekalsbeek.blogspot.com/2019/11/the-nutritional-thingy.html might help you along.