Side Effects of Metformin 500 mg Tablets

**Metformin is a medication primarily prescribed to people with type 2 diabetes to help lower their blood sugar 58.

** It is considered a first-line (first choice) medication because it is typically highly effective and has very few side effects. Metformin 500 mg is the lowest dose of the medication 8.

How Does Metformin Work?

Glucose, aka blood sugar, is the body's main source of fuel 5. The body gets glucose two ways: from the carbohydrates in food, and from the liver.

Once the body has converted the carbohydrates in food into glucose, the hormone insulin moves the glucose from the bloodstream into the cells, which use it for energy. But people with type 2 diabetes have become insensitive to insulin; their cells can't use it effectively, a condition called insulin resistance. This causes glucose to build up in the bloodstream, resulting in high blood sugar 5. Metformin increases the muscle cells' sensitivity to insulin, which lowers blood sugar, as explained by a November 2013 study published in Pharmacogenet Genomics 58.

At times when the body's cells aren't getting energy from food (such as between meals or overnight), the liver takes over the job of supplying the body with glucose 5. Metformin reduces the amount of glucose released by the liver, thereby keeping blood sugar levels from rising too much overnight 58.

Metformin Side Effects

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The typical starting dose for metformin is the lowest dose: 500 mg 8. According to Dr. Elizabeth Halprin, clinical director of adult diabetes at Harvard's Joslin Diabetes Center, this low dose helps reduce gastrointestinal (GI) side effects.

"If you start right at a full dose, you'll definitely get GI side effects," she says. "If you start with a low dose and taper up very slowly, like over four weeks, you may get mild symptoms, but they will generally go away.

You may get mild symptoms every [dose] escalation, but [metformin] is much better tolerated [if you build up slowly]." Taking metformin with food also helps minimize any adverse GI effects 8.

According to a study published in February 2012 by the American Diabetes Association (ADA), the most common metformin side effects include 8:

• Diarrhea
• Nausea
• Vomiting
• Gas
• Abdominal pain

Metformin and Hypoglycemia

Hypoglycemia, or low blood sugar, is common for people with diabetes 5. But the February 2012 ADA study noted that hypoglycemia is rarely a side effect for people taking metformin 8. This is because metformin does not increase insulin levels 8. Hypoglycemia is more likely to occur when metformin is combined with other types of diabetes medications, such as insulin injections or sulfonylureas (pills that increase insulin production) 8.

Metformin-Associated Lactic Acidosis (MALA)

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When the body uses glucose as energy, it also creates lactic acid. Lactic acid is best known as the substance that causes sore muscles after exercise.

Metformin increases the body's store of lactate — the underlying compound of lactic acid 8. Too much lactic acid in the blood can lead to a condition called lactic acidosis.

MALA is a very rare side effect. According to a study published in the February 2016 issue of Metabolism, MALA occurs in fewer than 10 people out of every 100,000 people per year. Though the risk of MALA is low, it is a serious condition and can be life-threatening.

The symptoms of MALA can be difficult to recognize because they typically look like the symptoms of other medical conditions. According to the FDA, the symptoms of lactic acidosis can include:

• Lethargy or unusual tiredness
• Nausea
• Vomiting
• Weakness
• Abdominal pain or stomach discomfort
• Difficulty breathing
• Muscle cramping
• Fast heart rate
• Diarrhea

MALA is very unlikely unless you have additional medical complications such as congestive heart failure or severe kidney or liver disease. Be sure to discuss these risks factors with your doctor.

Excessive alcohol use can also be a risk factor for MALA, as it further raises your risk for lactic acidosis, according to a small study published in the October 2016 issue of Scientific Reports.

Intravenous contrast dye (sometimes used in medical scans) can stress the kidneys and also increase the risk of MALA, according to a study published in the January 8, 2013 Canadian Medical Association Journal 9. Experts at the University of Michigan explain that, to reduce the risk of MALA and/or kidney damage, people taking metformin should stop the medication the day of their contrast study and wait 48 hours before resuming it 89.

Metformin and B12 Deficiency

Metformin use has been associated with an increased risk of vitamin B12 deficiency-related anemia 38. A study published in the April 2016 Canadian Medical Association Journal found that metformin is significantly associated with B12 deficiency 8. B12 is an important vitamin for your body, which uses it to make red blood cells. A lack of B12 can cause anemia.

Metformin Dosages

Metformin comes in 500 mg, 850 mg and 1000 mg doses, according to RxList.com 8.

The medication can be taken up to three times per day, but the maximum daily dose should never exceed 2550 mg. According to the ADA study, the higher the dosage, the higher the chance of adverse side effects.