Ten Myths About Metformin

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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 (Glucophage) bad for you? There is quite a bit of misinformation out there about this commonly used 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 myths.

  1. Metformin is bad for your kidneys. It’s not. What may be confusing folks here is that until 2016 patients with a creatinine level above 1.5 were advised not to take metformin. Metformin does not cause the kidney problems and in fact, 2016 labeling on Metformin was changed to indicate it should not be used only in those with late-stage chronic kidney disease stage IV or V.
  2. Metformin is bad for your liver. Truth is, it’s not. Metformin isn’t metabolized at all by the liver and instead is excreted unchanged in the urine. Metformin-induced liver injury is a rare, but possible adverse drug reaction that usually occurs at 4-8 weeks of therapy.
  3. Metformin is dangerous to take if you want to become pregnant. This is not true, and in fact may be the opposite. Metformin therapy during pregnancy in women with PCOS is associated with a reduction in miscarriage rate and gestational diabetes and did not adversely affect birth weight or development at 3 and 6 months of life.
  4. Metformin causes dementia. No. In fact a recent study of 17,000 diabetic vets found that taking metformin was associated with a lower risk of dementia than sulfonylureas like glyburide or glipizide. 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. Metformin has been suggested to exhibit cardioprotective effects in the setting of a heart attack. Metformin therapy is also associated with lower rates of death in patients affected by both diabetes and heart failure and reduced risk of cardiac failure morbidity and mortality in diabetic patients.
  6. Metformin causes cancer.  This is also not true and metformin appears to have a protective effect. In just one example the Women’s Health Initiative (WHI) found that metformin was associated with less cancer-related mortality in patients with diabetes. Metformin has also been shown to reduce recurrence of colorectal polyps suggesting a protective role in colon cancer.
  7. Metformin causes scary lactic acidosis. The risk of metformin causing acidosis of the blood is exceedingly rare. A Cochrane systematic review of 70,490 type 2 diabetics on metformin did not report a single case of metformin lactic acidosis. The risk of metformin causing lactic acidosis appears to be no greater than with non-metformin therapies.
  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. 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 and without end-stage kidney disease there is no risk and no need to discontinue metformin either prior to or following the administration of contrast media. In patients taking metformin who are known to 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.
  10. Metformin raises cholesterol. Nope! In fact, metformin has a beneficial impact on lipid (cholesterol) metabolism and lowers LDL cholesterol along with lowering triglycerides.

Dr. O

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