Metformin Side Effects

Metformin Side Effects

Metformin is an oral medication of the biguanid class. It is used for the treatment of type 2 diabetes and lowers the blood glucose (sugar). It is the first-line drug of choice for overweight and obese people. Metformin lowers insulin resistance. It increases the sensitivity of the liver, muscle, fat, and other tissues to the uptake and effects of insulin produced by the pancreas. This helps to lower the blood sugar level.

It can be used alone or as a part of combined therapy. As proven by clinical studies, Metformin helps to reduce complications of type 2 diabetes such as heart disease, blindness and kidney disease.

Metformin can also be used for treatment of women with polycystic ovary syndrome (PCOS).

Side effects

Like any medicine, Metformin has side effects. Some of them are quite common (e.g. diarrhea, nausea and vomiting) and some occur rarer (e.g. gas, weakness, indigestion, abdominal (or stomach) discomfort).

According to many clinical studies, 1 to 5% of patients experience side effects such as:

  • Taste changes (metallic taste in the mouth)
  • Abnormal stools
  • Muscle pain
  • Lightheadedness or dizziness
  • Difficulty breathing
  • Nail problems
  • Loss of appetite
  • Increased sweating
  • Flu-like symptoms, such as fever, muscle pain, chills, and weakness
  • Flushing(a reddening of the skin, especially in the face)
  • Feelings of a forcefully or rapidly beating heart (heart palpitations)
  • Asthenia
  • Unusual tiredness or weakness
  • General feeling of being unwell
  • Increased homocysteine levels
  • Malabsorption of vitamin B12 that can lead to megaloblastic anemia
  • Unusual drowsiness

The most serious and dangerous side effects of Metformin are

  • Hypoglycemia (low blood sugar)
  • Hyperglycemia (high blood sugar)
  • Lactic acidosis (increased lactic acid production)

Hypoglycemia develops when your blood sugar level drops too low to meet your needs. It can develop very quickly. Some of the symptoms of low blood sugar: sweating, shakiness, extreme hunger, dizziness, cold sweats, blurry vision, changes in behavior (such as irritability), loss of coordination, speaking difficulty, and seizures. If you do not quickly eat hard candy, drink juice, or ingest something with sugar in it, more severe symptoms may appear. These include sudden confusion and you may even faint.

The second possible serious side effect is hyperglycemia – a condition that can occur when your blood sugar level rises too high. In this case, you may experience increased hunger, very dry mouth, extreme thirst, increased urination, blurred vision, fatigue, shortness of breath, nausea or vomiting. If you do not treat this dangerous condition quickly, your body may dive into a condition known as diabetic ketoacidosis and you might start finding it very hard to breathe and even faint after a few moments.

The third possible and the most dangerous side effect is lactic acidosis. Signs of lactic acidosis include feeling tired or weak, muscle pain, breathing difficulty, abdominal pain (or stomach pain), feeling cold, cold or blue hands and feet, dizziness or lightheadedness, slow or irregular heartbeat, persistent nausea, vomiting, and abdominal pain, shortness of breath, an enlarged or tender liver, weight loss. This complication is very rare. Lactic acidosis does not develop in healthy people because their body can deal with lactic acid excess. Most of these cases seem to be related to comorbid conditions. Because Metformin decreases liver uptake of lactate, any condition that may precipitate lactic acidosis is a contraindication to the use of this drug. Alcoholism, heart failure, respiratory disease (due to inadequate oxygenation of tissues) and kidney disease are the common causes of increased lactic acid production.

This medicine can also cause such allergic reactions as:

  • an unexplained skin rash
  • itching
  • hives
  • wheezing or trouble breathing
  • unexplained swelling of the mouth, face, lips, or tongue
  • tightness in the chest

Side effects in children

According to clinical trials, Metformin have the same side effects in children with type 2 diabetes as in similar adults.


You may never experience any of the side effects listed above. Your doctor cannot predict your body’s reaction to Metformin until you have tried it. That is why you should immediately inform your doctor of any changes in your health condition after taking Metformin. Therefore, when you feel something is wrong, ask your doctor for advice and he or she will diagnose if your problem is connected with the medicine intake. You should also be careful because some of the side effects of Metformin require urgent medical attention.