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Why Does Metformin Cause Diarrhea?

Why Does Metformin Cause Diarrhea?

With an estimated 31 million Americans suffering from Type 2 diabetes according to the American Diabetes Association, many people are in need of treatment options that can effectively control the condition. Although many people are familiar with Type 1 diabetes, which is a condition in which patients do not produce enough insulin, Type 2 diabetes is actually much more common. Type 2 diabetes is heavily influenced by lifestyle factors like being overweight, eating an unhealthy diet, and leading a sedentary lifestyle, and the condition is characterized by insulin resistance. Patients with insulin resistance have high blood sugar levels because their bodies ignore instructions from the insulin hormone to use sugar in the blood for energy. While lifestyle changes like eating a healthy diet, getting more exercise, and losing weight are an important first step in the treatment of Type 2 diabetes, other patients may require medication to get their condition under control. In these situations,  prescription drugs like metformin can be used in combination with lifestyle changes to treat Type 2 diabetes. Metformin is a highly effective drug for the treatment of Type 2 diabetes, but it causes gastrointestinal side effects like diarrhea in about half of the people who take it. Why does metformin cause diarrhea, and is there anything patients can do to avoid it? 

What is metformin?

Metformin is a generic prescription drug belonging to a class of medications called biguanides. Metformin is commonly used to treat Type 2 diabetes; in fact, metformin is the most commonly prescribed medication for Type 2 diabetes in the world. Although biguanides were once commonly used for the treatment of Type 2 diabetes, today, the only other biguanides that remain on the market are used to treat malaria.  Metformin has been used in the United States since it was first approved by the U.S. Food and Drug Administration (FDA) in 1995. Today, metformin can be purchased in both immediate and extended-release formulas and is available under the brand names Glucophage and Glucophage XR.

What conditions are treated with metformin?

An estimated ten percent of Americans have diabetes, which exists in two types: Type 1 and Type 2. Type 1 diabetes, or juvenile diabetes, is defined by the body’s failure to produce enough insulin, while Type 2 diabetes results from insulin resistance. Most people (about 90 percent) with diabetes have Type 2 diabetes, which is heavily influenced by lifestyle factors such as weight, diet, and activity level. People with both forms of diabetes cannot properly utilize the glucose, or sugar, in the foods we consume and turn it into energy. In a healthy body, our digestive systems break down the food we eat into glucose, which is released into the bloodstream. As glucose enters the bloodstream,the levels of sugar in the blood rise, causing the pancreas to start to release insulin. Insulin is a hormone that is responsible for directing the body to begin converting the sugar in the blood into energy. In people with Type 2 diabetes, the directions given by insulin are ignored, so levels of sugar in the blood remain high for a prolonged period of time, causing potentially serious complications. Metformin helps to increase the body’s sensitivity to insulin, which allows glucose in the blood to be used for energy. Although some people are able to control their Type 2 diabetes through lifestyle changes alone, others require medications like metformin in order to avoid dangerous health effects and complications. Serious conditions and complications associated with uncontrolled levels of high blood sugar include:

  • Damage to the blood vessels of the eyes (retinopathy)
  • Increased risk of heart problems like heart disease
  • Increased risk of kidney disease
  • Nerve damage in the feet and hands (neuropathy)

What are the side effects of metformin?

More patients take metformin for the treatment of Type 2 diabetes than any other medication, but the drug has the lowest adherence rate of any Type 2 diabetes medications, according to one study. Metformin was designed to be used long term, but the high incidence of unpleasant side effects can substantially alter patients’ quality of life and willingness to take the medication. While the side effects associated with metformin can be particularly uncomfortable and have a more severe presentation, the drug has fewer side effects than other Type 2 diabetes and prediabetes medications. There are ways to diminish the likelihood of experiencing side effects while taking metformin, as outlined below. Common side effects associated with metformin that usually do not require medical attention include:

  • Diarrhea
  • Stomach pain
  • Bloating not from weight gain
  • Unpleasant metallic taste in the mouth
  • Nausea or vomiting
  • Heartburn
  • Gas
  • Constipation
  • Headache
  • Weight loss

Most of the side effects associated with metformin are common and do not require medical attention, but other side effects of the drug can be serious. Although these side effects are rare, they have occurred in some patients, and they require immediate medical attention. Patients experiencing lactic acidosis, anemia (low levels of iron in the blood), and hypoglycemia (low blood sugar) while taking metformin should seek immediate medical attention. 

Why does metformin cause diarrhea?

Metformin is an extremely effective drug for the treatment of Type 2 diabetes, but the high incidence of side effects, particularly gastrointestinal side effects like diarrhea, can cause patients to stop taking the medication. Numerous studies have attempted to discern why metformin causes diarrhea and other gastrointestinal side effects because, as one study notes, quality of life and treatment adherence is negatively affected in patients with Type 2 diabetes who are taking metformin. Although the exact mechanism of metformin that causes diarrhea and other gastrointestinal side effects is still unclear, researchers have developed several possible explanations, including stimulation of intestinal secretion of serotonin, alteration in incretin and metabolism of glucose, and malabsorption of bile salts. In reality, it is likely a combination of all of these factors, as each has been shown to cause diarrhea on its own. Although most patients find that their diarrhea and other gastrointestinal side effects are reduced as their bodies become more accustomed to metformin, other patients experience gastrointestinal side effects for their entire course of treatment. 

How can you avoid metformin side effects?

If taking metformin is causing troublesome side effects, it may be possible to minimize or avoid these side effects with some simple changes. First, if you have just begun taking metformin or have recently adjusted your dose, give your body about two weeks to adjust to the medication. Many people find that their symptoms disappear after about two weeks. If you continue to experience diarrhea and other gastrointestinal side effects after two weeks, try taking your medication with a meal. Taking metformin with a meal helps to slow the body’s absorption of the drug, which reduces the likelihood of side effects. Take metformin with your biggest meal if you take it only once a day, and take it at breakfast and dinner if you take the medication twice per day. Although many patients initially take the immediate release form of the medication due to its lower cost, switching to the extended release form of metformin can help to prevent side effects as well. Speak to your doctor to find out if adding a dietary supplement might be able to help mitigate certain side effects of the medication as well. 

Sources:

https://www.healthline.com/health/diabetes/metformin-side-effects 

https://www.healthline.com/health-news/why-so-many-people-with-diabetes-stop-taking-metformin 

https://www.cdc.gov/diabetes/basics/type2.html 

https://www.cdc.gov/diabetes/basics/diabetes.html 

https://www.diabetes.org/resources/statistics/statistics-about-diabetes 

https://medlineplus.gov/druginfo/meds/a696005.html 

https://www.verywellhealth.com/biguanides-diabetes-medications-1087355 

https://www.tandfonline.com/doi/full/10.3109/10717544.2015.1089957 

https://dom-pubs.onlinelibrary.wiley.com/doi/abs/10.1111/dom.13160 

https://www.healthline.com/health/grapefruit-and-metformin 

https://www.rxlist.com/consumer_metformin/drugs-condition.htm 

https://www.rxlist.com/consumer_metformin/drugs-condition.htm#what_are_warnings_and_precautions_for_metformin 

https://www.alliedacademies.org/articles/metformin-and-its-gastrointestinal-problems-a-review-10324.html