Side Effects and Risk Factors of Metformin

Metformin is a prescription drug used to treat type 2 diabetes by help lowering your blood sugar levels to a target range. This is also used in treating PCOS (polycystic ovarian syndrome).

Updated: December 4, 2017

Metformin is a prescription drug used to treat type 2 diabetes by help lowering your blood sugar levels to a target range. This is also used in treating  PCOS (polycystic ovarian syndrome).
Metformin can cause mild and serious side effects, which are the same in men and women. The side effects include diabetic neuropathy, brain fog, and digestive issues. It belongs to a class of medications called biguanides. Most prescribed names in metformin category include fortamet, glucophage, glucophage XR, riomet, glumetza, formin, daomet SR, met-500 and bigomet.

Side Effects of Metformin:

Type 2 Diabetes is a chronic disease that requires lifelong management with medication. Metformin if taken for a longer period of time, along with its benefits it is more likely to create side effects.

The most common side effects include:

  • Reduced appetite
  • Stomach or abdominal discomfort
  • Cough or hoarseness of voice
  • Tingling or numbness in the palms and feet
  • Diarrhea
  • Fatigue
  • Macrocytic anemia
  • Pain in the lower back or in the flanks
  • Muscle pain or cramping
  • Hair loss
  • Blurred vision
  • Weight gain
  • Anxiety
  • Shallow breathing
  • Painful or difficult urination

Serious side effects of metformin:

These include:

Lactic acidosis:

Lactic acidosis is a rare but serious problem that can occur due to a buildup of metformin in your body.  It is a medical emergency that must be treated right away in the hospital.

The symptoms include:

  •     extreme tiredness
  •     weakness
  •     decreased appetite
  •     nausea
  •     vomiting
  •     trouble breathing
  •     dizziness
  •     lightheadedness
  •     a fast or slow heart rate
  •     feeling cold
  •     muscle pain
  •     flushing (sudden reddening and warmth in your skin)
  •     stomach pain with any of these other symptoms


Metformin can decrease the levels of vitamin B-12 in your body. This can cause anemia in rare cases. Vitamin B-12 levels can be improved by taking vitamin B-12 supplements.

The more common symptoms of anemia include:

  •     tiredness
  •     dizziness
  •     lightheadedness

Check your red blood cell levels if you have these symptoms.


Metformin alone does not cause hypoglycemia. It may develop hypoglycemia if taken in combination with other diabetes medications, excessive alcohol intake, a poor diet and strenuous exercise.

Symptoms of hypoglycemia include:

  •     weakness
  •     tiredness
  •     nausea
  •     vomiting
  •     stomach pain
  •     dizziness
  •     lightheadedness
  •     abnormally fast or slow heartbeat

To help prevent hypoglycemia, take your medications on schedule, follow a well-balanced diet and exercise as directed by your doctor.

Risk Factors of Taking Metformin:

There are several factors which can raise the risk of lactic acidosis while you take metformin. These include:

Kidney problems:

One of the most important role of kidney in your body is to filter waste materials from the blood and expel them from the body as urine. If your kidneys are not working properly, they can not remove metformin from your body resulting in higher levels of metformin in your system. This raises your risk of lactic acidosis.
If you have mild or moderate kidney problems, a lower dosage of metformin can be prescribed. But if you have severe kidney problems or are 80 years or older, metformin may not be right for you. You should do a kidney function test before starting metformin. This test should be done every year after the age of 80.

Heart problems:

If you have acute heart failure or have recently had a heart attack, metformin is not recommended for you. In this condition your heart may not be able to send enough blood to your kidneys which would prevent your kidneys from removing metformin from your body as well as they normally would, raising your risk of lactic acidosis.

Liver problems:

One of the function of liver is to clears lactic acid from your body. If you have severe liver problems, your lever would not be able to remove lactic acid from your body which could lead to a buildup of lactic acid. Lactic acid buildup raises your risk of lactic acidosis. In addition metformin also raises your risk. So its not advisable to take metformin if you have liver issues.


Drinking alcohol while taking metformin raises your risk of hypoglycemia. As it increases lactic acid levels in your body, it also raises your risk of lactic acidosis.

Surgical or radiologic procedures:

Metformin reacts adversely and severely with certain drugs that are given prior to imaging or CT scan procedures. If you need to get a scan done, you should stop taking metformin for a few days before and after the scan.
If you have any of the above issue, discuss it with your doctor before starting metformin.

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