No link between men taking diabetes drug and birth defects, large study confirms

The diabetes drug metformin has not been linked to birth defects in the children of men who used it around the time of conception, a large, international study has shown.

Metformin is a drug used to treat type 2 diabetes, a condition where not enough insulin is made by the body, resulting in high blood glucose. Previous research published in the Annals of Internal Medicine, conducted in 2022, found metformin was linked to a greater risk of defects in male babies where the fathers were taking metformin. However, no other study has been able to confirm this association. Recently published in the BMJ, a much larger study looked at over three million pregnancies in Norway and Taiwan, and found no correlation between birth defects and the use of metformin by fathers during the three months prior to conception, the period of sperm development.

In a statement regarding the new research, Professor Allan Pacey, professor of andrology at the University of Manchester and Trustee of PET (the Progress Educational Trust), said, 'By using data from two different populations in Norway and Taiwan, the new paper has taken the analysis one step further and have concluded that no real link exists between a father's metformin use and any birth defects in his sons. This makes sense because there was never any plausible biological mechanism which might have led us to this conclusion.

'I hope that this new study provides further reassurance that metformin is a safe drug that can be used for the control of type 2 diabetes in men who wish to become fathers.'

The results showed congenital defects in five percent of offspring from fathers who took metformin three months prior to conception in Norway compared to 3.9 percent of offspring from fathers who did not take the drug, and 3.4 percent compared to 3.1 percent respectively in Taiwan. After restricting the analyses to fathers with type 2 diabetes, as well as other important variables such as age and related conditions, the study found no increased risk of any congenital defects in children from fathers who used metformin during the sperm development period prior to conception.

In June, another study in the Annals of Internal Medicine analysed data from Israel and countered that despite there being a higher rate of birth defects in children of men who use metformin, the causality may be from diabetes and cardiovascular comorbidities, instead of a side effect of the drug (see BioNews 1244).