The Side Effects Of The Diabetes Drug Metformin

Metformin is an oral prescription medication that helps people with Type 2 diabetes manage blood glucose levels. It is in the biguanides class of Type 2 diabetes drugs and controls blood glucose by decreasing the amount of glucose that the liver produces. In general, patients tolerate metformin well, but side effects occur in about 20 percent of those taking the drug.

Gastrointestinal Side Effects

According to the "Physicians' Desk Reference," patients who take metformin most commonly experience gastrointestinal side effects. These effects include diarrhea, nausea, vomiting, abdominal bloating, flatulence and anorexia. These effects are more prevalent in the early stage of metformin therapy, and disappear as treatment continues. About 4 percent of patients on metformin therapy stop taking the drug because of gastrointestinal side effects.

Metabolic Side Effects

The U.S. Food and Drug Administration has estimated that lactic acidosis is a side effect in 5 out of every 100,000 people who use metformin for any length of time. Lactic acidosis is a potentially fatal medical emergency that occurs when lactic acid builds up in the bloodstream. Patients who experience weakness, fatigue, unusual muscle pain, or unusual stomach distress while taking metformin may have lactic acidosis. Even though this side effect occurs very rarely in healthy patients, it delayed the launch of metformin in the United States until 1995. People in other countries around the world were using metformin years before its U.S. introduction. Doctors advise that people who have congestive heart failure, kidney disease or liver disease should not take metformin because these health conditions increase the risk of lactic acidosis.

Hypoglycemia is another uncommon metabolic side effect. The risk of hypoglycemia increases with strenuous exercise, lower caloric intake and consumption of alcohol.

Hematologic (Blood Cell) Side Effects

About 30 percent of patients taking metformin have experienced diminished absorption of vitamin B12 from the intestine. Vitamin B12 promotes the maturation of red blood cells, and a deficiency of B12 leads to anemia. Certain cells in the intestine secrete a protein called intrinsic factor, which allows the body to absorb vitamin B12. Metformin may interfere with intrinsic factor secretion and this interference leads to diminished B12 absorption. It is possible that the patient may continue to use metformin, but a dietary supplement of vitamin B12 is necessary.
Taking metformin has also led to megaloblastic anemia, a condition in which patients show enlarged and immature red blood cells.