Question & Answer

Q: In your article “Metformin: First-Choice Drug for Type 2 Diabetes” in the August 2018 issue, you did not mention that diarrhea is one of metformin’s adverse effects. I know two people who developed severe diarrhea while taking the drug and had to stop taking it. Can you provide more information about this adverse drug effect?

A: You are correct — diarrhea is one of the most common adverse effects of metformin (FORTAMET, GLUCOPHAGE, GLUCOPHAGE XR, GLUMETZA, RIOMET).[1] In one preapproval clinical trial of the brand-name drug Glucophage, an immediate-release form of metformin, 53 percent of subjects receiving the drug developed diarrhea, whereas only 12 percent of those receiving a placebo reported diarrhea. The diarrhea was severe enough to require discontinuation of the drug in 6 percent of subjects.

Importantly, diarrhea occurs less frequently with Glucophage XR, an extended-release form of metformin. In clinical trials of Glucophage XR, only 10 percent of patients receiving the drug and 3 percent receiving a placebo developed diarrhea. Of those receiving the drug, less than 1 percent discontinued use because of diarrhea.

In addition to diarrhea, metformin also can cause abdominal pain, indigestion, nausea, vomiting, flatulence and an unpleasant metallic taste. These adverse effects generally go away after taking the medicine for awhile. Taking metformin with meals can help reduce these effects. Tell your doctor if the adverse effects bother you a lot, last for more than a few weeks, come back after they’ve gone away or start later during treatment. You may need a lower dose or need to stop taking the medicine for a short period or for good.

References

[1] Bristol-Myers Squibb Company. Label: metformin (GLUCOPHAGE and GLUCOPHAGE XR). May 2018. https://www.accessdata.fda.gov/drugsatfda_docs/label/2018/020357s034,021202s018lbl.pdf. Accessed October 10, 2018.