Is it safe to take metformin while pregnant or breastfeeding?

No: Metformin is an oral medication used to treat diabetes and pcos (polycystic ovary syndrome). At this time, there are no studies that document metformin's safety in pregnancy or nursing. Current recommendations are to use alternative medications.

Very safe: Metformin has been looked at and found to be very safe during breastfeeding. A small amount does enter the milk, the relative infant dose is 0.3-0.7% of mom's dose. It is considered a level 1, the safest category for breast feeding. See:hale, t;medications and mothers milk, hale publishing, 16ed, 2012, pp744-745.