10 Big Myths About Metformin, the Popular Diabetes Drug

Dr. Sharon Orrange
Dr. Orrange is an Associate Professor of Clinical Medicine in the Division of Geriatric, Hospitalist and General Internal Medicine at the Keck School of Medicine of USC.
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Is metformin bad for you? There is quite a bit of misinformation out there about this popular medication. Metformin therapy may cause diarrhea and lower vitamin B12 levels, but most things you hear about metformin aren’t true.

Here are some common metformin (Glucophage) myths.


1) Metformin is bad for your kidneys.

It’s not. There may some confusion here because up until 2016, patients with higher creatinine levels (above 1.5 mg/dL) were advised not to take metformin. But metformin, in fact, does not cause kidney problems, and that recommendation has since changed. Now, labels for metformin say that only patients with late-stage chronic kidney disease (stage IV or V) should not use the medication.


2) Metformin is bad for your liver.

The truth is, it’s not. The liver isn’t involved in processing and metabolizing metformin at all. Instead, metformin leaves the body unchanged in the urine. In fact, metformin could be beneficial to some patients with certain liver diseases. Metformin-induced liver injury is a very rare, but possible adverse drug reaction that usually occurs at 4 to 8 weeks of therapy while taking other drugs that potentially damage the liver.


3) Metformin is dangerous to take during pregnancy.

This is not true. In fact, it may be the opposite. For example, one study found that metformin therapy during pregnancy in women with polycystic ovarian syndrome (PCOS) was associated with a reduced rate of miscarriage and gestational diabetes. Also good to know: the same study showed that taking metformin did not adversely affect birth weight or development of the newborn at 3 and 6 months of life.

4) Metformin causes dementia.

No. In fact, a recent study of 17,000 veterans with diabetes found that taking metformin was associated with a lower risk of dementia than sulfonylurea drugs (e.g. glyburide, glipizide). And other studies have shown metformin use to be associated with reduced rates of dementia and improved cognitive function.


5) Metformin is bad for your heart.

This is one I hear quite a bit from patients, and it’s not true. Studies suggest that metformin exhibits heart-protective effects in the setting of a heart attack. Metformin therapy is also associated with a reduced risk of death and disease in patients affected by both diabetes and heart failure.


6) Metformin causes scary lactic acidosis.

The risk of metformin causing lactic acidosis of the blood is exceedingly rare. A Cochrane systematic review of 70,490 patients with type 2 diabetes on metformin did not report a single case of metformin-induced lactic acidosis. The risk of metformin causing lactic acidosis appears to be no greater than that of non-metformin therapies.

7) Metformin raises cholesterol.

Nope! In fact, metformin has a beneficial impact on lipid (cholesterol) metabolism and lowers LDL cholesterol along with triglycerides.


8) Metformin is bad for the pancreas.

Metformin is not a known cause of acute pancreatitis and LOWERS, not raises, the risk of pancreatic cancer.


9) Metformin causes cancer.  

This is also not true. Metformin appears to be protective. In just one example, the Women’s Health Initiative (WHI) found that metformin was associated with less cancer-related death in patients with diabetes. Studies show that metformin also reduces the reappearance of colorectal polyps, which may turn into cancer, suggesting that metformin plays a protective role in colon cancer.


10) You can’t have a CT scan with contrast if taking metformin.

Intravenous contrast is often given prior to CT scan imaging. In patients with no evidence of acute kidney injury or end-stage kidney disease, there’s no need to discontinue metformin either prior to or following the administration of contrast media. In patients taking metformin who have acute kidney injury or severe chronic kidney disease (stage IV or stage V), metformin should be temporarily discontinued at the time of or prior to the procedure, and withheld for 48 hours subsequent to the procedure.


Dr. O

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