Most people have mild side effects with metformin. This drug is safe for long term use; however it should be accompanied by a diet and exercise plan. In addition, this medication may not work as well over time as your body adapts to it.
If you become elderly, while taking metformin, you should have regular kidney function tests. If there is decreased kidney function, taking metformin could put you at risk for lactic acidosis, which is very serious and sometimes fatal. Metformin should be temporarily discontinued in people who are having radiologic tests that require iodinated contrast materials, as this can cause problems with renal function. If you start to drink alcohol excessively, you should no longer take this medication.