Dads’ metformin use linked to birth defects

Close-up on man’s hands pouring white tablets from a pill bottle into his palm.

April 7, 2022—For men who are trying to father a baby, taking the diabetes drug metformin during a roughly 90-day period before they conceive appears to increase the risk of genital birth defects in their male children. That's according to a new study in the Annals of Internal Medicine.

Metformin is often used along with diet, exercise and weight control to lower blood sugar levels in people who have type 2 diabetes, according to the American Diabetes Association. It can help you stay healthy. But researchers have linked it to a risk of birth defects in the children of men who take this medication.

The facts on metformin and birth defects

Researchers looked at data on more than a million babies born in Denmark. They compared the risk of birth defects among babies whose fathers took one of three diabetes medicines: metformin, insulin or a sulfonylurea.

The researchers found that:

  • Children whose fathers took metformin before conception had an increased risk of birth defects, specifically genital birth defects in boys.
  • The increased risk of birth defects occurred only if the men used metformin during the three months prior to conceiving the child. That is about how long sperm stay viable in a man's body.
  • Men who used insulin before conceiving did not have an increased chance of having a child with a birth defect. (Not enough men took sulfonylureas to show if that drug affected the risk of birth defects.)

This study does not prove that metformin causes birth defects. We need more research to confirm the findings and to find out what caused the apparent raised risk of birth defects, the authors said.

Weigh your risks

Men who take metformin and want to have children should talk to their doctors about whether to use another treatment when they're trying to conceive. But diabetes itself can affect men's sperm quality. That can affect their chances of having a child.

Also, diabetes raises the risk for other serious health problems, like heart disease. It's important to keep the disease under control. Medications such as metformin can help.

Your doctor can help you understand the risks and benefits of your treatment so that you can make the choice that's best for you. And you can learn more about living well with diabetes in our Diabetes topic center.

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