What is Metformin?
Generic metformin tablets, sold in the United Kingdom.
Credit: Public domain.

Metformin is a prescription drug used primarily in the treatment of Type II diabetes. It can be used on its own or combined with other medications. In the United States, it is sold under the brand names Fortamet, Glucophage, Glumetza and Riomet. 

"Metformin is very often prescribed as the first step in a diabetic's regime," said Ken Sternfeld, a New York-based pharmacist.

"When you're diabetic you lose the ability to use the insulin you need to offset the food," Sternfeld explained. "If you eat a carb or sugar that can't be metabolized or offset by the insulin you produce, your sugar levels will be higher. Metformin and drugs in that category will help your body better metabolize that food so that insulin levels will be able to stay more in line."

Metformin aims to decrease glucose production in the liver, consequently lowering the levels of glucose in the bloodstream. It also changes the way that your blood cells react to insulin. "It makes them more sensitive to insulin," said Dr. Stephen Neabore, a primary care doctor at the Barnard Medical Center in Washington, D.C. "It makes the same amount of insulin work better. It transports the insulin to the cells in a more effective way." 

Metformin may have a preventive health role, as well. New research presented at the American Diabetes Association 2017 Scientific Sessions showed that long-term use of metformin is particularly useful in preventing the onset of type II diabetes in women who have suffered from gestational diabetes. 

Because metformin changes the way the body uses insulin, it is not used to treat Type I diabetes, a condition in which the body does not produce insulin at all.

Metformin is sometimes prescribed to treat polycystic ovarian syndrome (PCOS), according to Neabore. "I can't think of a time when I've seen major side effects," he said. Clinical studies by the University of Chicago have supported its efficacy. Using metformin to treat PCOS is not yet approved by the Federal Drug Administration (FDA), however. Neabore recommends talking to a doctor about the drug's potential in this category.

According to the University of Chicago Medical Center, lowering insulin levels also lowers the amount of testosterone produced, thus theoretically decreasing the symptoms of PCOS that are associated with excess testosterone. Metformin may help restore regular menstrual cycles and improve metabolism, thus possibly leading to weight loss in women with PCOS. It may also help reduce the chance of miscarriage or gestational diabetes and improve the chance of successful in-vitro fertilization (IVF), though according to the NIH, research is inconclusive on all of these topics.

Sternfeld emphasized the importance of adhering to the metformin dosage and schedule laid out by your doctor and also discussing it with your pharmacist. "Metformin is a maintenance drug and you need to take it as prescribed forever," he said. "If you don't take it at that dosage level, your sugar level will go up. There's a direct relationship between adherence to the drug and disease state. If you don't manage your sugar levels, you're not just looking at being diabetic but at being someone who has multiple blood sugar problems." 

Metformin can be taken as a tablet, an extended-release oral tablet or a liquid. Extended-release tablets should be swallowed, not chewed, crushed or split. The regular tablet is taken with meals two or three times a day, the extended-release tablet is taken once a day with a meal in the evening, and the liquid is usually taken with meals once or twice a day. "Its effects can greatly depend on the time of day you take it. Patients are always advised to take it after meals to avoid stomach distress," Sternfeld said. 

Doctors often start patients on low doses of metformin and gradually increase the dosage. "If you start someone on too high a dose, they may have severe diarrhea," Neabore said. Patients must carefully monitor blood sugar while taking metformin so that doctors will be able to determine how well the drug is working. The NIH stresses that patients should not stop taking metformin without consulting a doctor, even if they feel well. Metformin cannot cure diabetes, only help control it.

In the case of a missed dose, the patient should take the missed dose as soon as he or she remembers it, unless it is almost time for the next dose. In that case, the patient should skip the missed dose and continue on the regular dosing schedule. The NIH says that patients should not take a double dose to make up for a skipped one.

It is important for diabetic patients to follow a healthy eating and exercise routine as outlined by their doctor, Neabore said. "We recommend lifestyle changes as a primary intervention or at least along with medication," he said. In rare cases, serious and sustained lifestyle changes may even change the amount of metformin a patient may need in the future. "You might be able to reduce the dose or even discontinue it eventually," he said. "But lifestyle changes take some time and in the meantime it can be good to take medicines."

In the case of eating or exercising more or less than usual, a doctor should be informed. Such change can affect blood sugar levels, and doctors will provide specific instructions should this happen.

Drinking alcohol can potentially lower blood sugar levels, so it is important for patients to talk to a doctor about how much alcohol, if any, is safe to drink while taking metformin.

"The most common side effect of metformin is stomach distress — diarrhea, bloating, stomach pain, gas, indigestion, constipation," Sternfeld said. 

According to the NIH, other common side effects of metformin include:

  • unpleasant metallic taste
  • heartburn
  • headache
  • skin flushing
  • changes in finger or toenails
  • muscle pain

If any of these side effects persist, become severe, disappear and then return, or only appear after taking metformin for a long time, a doctor should be consulted.

More serious side effects are chest pain and rash. If these side effects occur, patients should immediately consult a doctor or seek emergency treatment. Patients should talk to their doctor and pharmacist about other risks of metformin. Before beginning metformin they should talk to their pharmacist about managing side effects and about any other drugs they are currently taking to avoid bad reactions, Sternfeld said. 

The NIH notes that metformin may rarely cause lactic acidosis, a serious, life-threatening condition. People over 80 years old who have had a heart attack, stroke, diabetic ketoacidosis, coma, or heart, kidney or liver disease should talk to their doctors about this risk of taking metformin.

Drinking alcohol can also increase the risk of lactic acidosis.

The research is inconclusive on whether or not metformin is safe to take during pregnancy. For example, the Mayo Clinic suggests that it is safe, while a 2008 study in the U.S. National Library of Medicine says, "is currently recommended that metformin be discontinued with the first positive pregnancy test result." Before getting a prescription, women should tell their doctors if they are pregnant, breast-feeding, or planning to become pregnant. If they get pregnant while taking metformin, a doctor should be informed immediately.

Though not categorized as a controlled substance, it is possible to overdose on metformin. According to the NIH, symptoms of overdose include:

  • hypoglycemia and its symptoms
  • extreme tiredness
  • weakness
  • discomfort
  • vomiting
  • nausea
  • stomach pain
  • decreased appetite
  • deep, rapid breathing
  • shortness of breath
  • dizziness
  • lightheadedness
  • abnormally fast or slow heartbeat
  • flushing of the skin
  • muscle pain
  • feeling cold

In the case of overdose, patients should contact their local poison control center. If the patient isn't breathing or has collapsed, call 911. Patients should go over dosing instructions and requirements thoroughly with a pharmacist to help avoid risk of overdose, Sternfeld said. 

A 2017 study published in Pediatrics found that metformin might be helpful in treating the effects childhood obesity in prepubescent children. Overweight prepubescent boys who took metformin for six months saw improvement in insulin sensitivity and other inflammatory and cardiovascular-related obesity parameters. Similar results might be achieved through lifestyle changes, however. Pubescent children did not see any results.

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