Metformin Warnings and Precautions
Some metformin warnings and precautions relate to monitoring your liver function while taking metformin, the possibility of the medication decreasing your B12 levels, and the potential for metformin to cause low blood sugar. Prior to taking metformin, you should talk to your healthcare provider about any health conditions you might have, such as kidney or liver problems, congestive heart failure, or low vitamin B12 levels.
- Kidney problems, including kidney failure (renal failure)
- Liver problems, including liver failure or cirrhosis
- Low vitamin B12 levels (pernicious anemia)
- Congestive heart failure (CHF)
- Had a heart attack or stroke
- An upcoming surgery or procedure (including x-rays or other radiology procedures)
- Any allergies, including allergies to foods, dyes, or preservatives.
- Are pregnant or thinking of becoming pregnant
- Are breastfeeding
- Drink alcohol regularly.
- Very rarely, metformin may cause a life-threatening condition called lactic acidosis. Your risk of lactic acidosis increases with other medical conditions, including congestive heart failure (CHF), kidney failure, and liver problems, including liver failure and cirrhosis (see Metformin and Lactic Acidosis for more information, including possible symptoms of lactic acidosis).
- Drinking alcohol can increase your risk of lactic acidosis. Drinking large amounts of alcohol on a regular basis or drinking a large amount of alcohol at once (binge drinking) should be avoided while taking metformin (see Metformin and Alcohol).
- Since liver disease (including liver failure and cirrhosis) can increase your risk of lactic acidosis, you should not take metformin if your liver is not functioning normally.
- Your kidney function needs to be monitored while you are taking metformin. This means that you should have blood tests to check your kidneys before you start metformin and then at least once every year. If your kidney function is very poor, you should not take metformin due to increased risk of lactic acidosis.
- Taking metformin and contrast dye at the same time can increase your risk of kidney damage. Contrast dye is used for certain radiology procedures, including some x-rays, CT scans, and heart catheterizations (see Metformin and Contrast Medium for more information). Also, metformin should be temporarily stopped for most major surgeries and should be restarted when you are eating normally again.
- Fever, infections, injury, or surgery can temporarily increase your blood sugar, even in people with well-controlled diabetes. Metformin may not be enough to treat your diabetes at these times, and the use of insulin may be required.
Contact your healthcare provider if you have a fever, infection, injury, or will be having surgery. Also, make sure you know the symptoms of high blood sugar and how to check your blood sugar levels (see Metformin and Blood Sugar for more information).
- Let your healthcare provider know if you drink a much lower amount of liquid than normal or if you have an illness that causes severe vomiting, diarrhea, or fever. These conditions can lead to severe dehydration (loss of water in your body). You may need to stop taking metformin for a short time.
- Metformin can decrease your levels of vitamin B12. Your healthcare provider should monitor your vitamin B12 levels, especially if you have a vitamin B12 deficiency (including pernicious anemia).
- Metformin can interact with certain medications (see Metformin Drug Interactions).
- Metformin is considered a pregnancy Category B medication. This means that it is probably safe for use in pregnant women, although the full risks of metformin during pregnancy are not known. Talk to your healthcare provider before taking metformin during pregnancy (see Metformin and Pregnancy).
- Metformin passes through breast milk. Therefore, if you are breastfeeding or plan to start breastfeeding, be sure to talk with your healthcare provider about this.
- Rarely, metformin can cause low blood sugar (hypoglycemia). This usually occurs when metformin is combined with other diabetes medications. Low blood sugar is reported more frequently in elderly people and in people with adrenal, pituitary, liver, or kidney problems -- as well as during fasting before surgery and after prolonged exercise.
Low blood sugar symptoms may include irritability, trembling, cold sweats, or blurry vision, among other things (see Metformin and Blood Sugar for more information).