Metformin: Is it Safe for Breastfeeding?

"Do I have to wean before I resume metformin?" is, perhaps, one of the most common questions posed by breastfeeding mothers suffering from PCOS. Fortunately, the answer to this question is a resounding "no," and that answer is supported by considerable research.

Benefits of Metformin
Metformin (a.k.a. glucophage), is an oral hypoglycemic drug used in the treatment of type II diabetes as well as polycystic ovarian syndrome and other diseases featuring insulin resistance. Though its exact action is uncertain, researchers believe that metformin functions by decreasing the intestinal absorption of glucose as well as increasing peripheral glucose uptake which may improve insulin sensitivity.

While not all women suffering from PCOS may test "insulin resistant," it is widely accepted that insulin resistance plays a key role in the syndrome. Metformin treatment is now becoming the most popular treatment for women suffering from the syndrome, as treatment often mitigates many of the syndrome's symptoms such as amennhorrea and anovulation. Cardiovascular health is also improved in women with PCOS who are treated with metformin.

Some women with PCOS may suffer from low milk supply, though it should be noted that the vast majority of mothers with PCOS exhibit adequate or even over supply. There is anecdotal evidence that metformin may increase milk production among women suffering from low supply directly related to the syndrome. However, the conditions contributing to an individual mother's milk supply can vary (scheduled feedings, early supplementation, poor latch etc.), and it should not be assumed that PCOS is the only, or even primary cause of low supply.

On the subject of metformin, insulin resistance and milk supply, Hillary Jacobson, author of Mother Food for Breastfeeding Mothers writes:
Metformin (Glucophage) is showing excellent results in the treatment of insulin resistance. It can be taken while breastfeeding under your doctor's supervision. Metformin may lead to an increase in mammary tissue, and to an increase of milk production.Though anecdotal evidence does imply that metformin may increase milk supply, as of the date of writing, no researchers have examined this connection in a clinical setting so Jacobson's proposition has not been proven, nor has it been disproven.

Safety of Metformin
Though benefits of metformin treatment to the polycystic mother are clear, some mothers and doctors are still concerned about the safety of the drug for the breastfed baby and child. While it is certainly the case that metformin should be taken under a doctor's supervision, and that every patient should be evaluated on an individual level, the vast majority of current research indicates that metformin is safe for the breastfeeding dyad.

In a 2002 study, noted lactational pharmacology researcher and author of Medications and Mothers Milk Dr. Thomas Hale, found that while metformin is transmitted to the infant via breastmilk, it is in such low concentrations that it does not pose a risk to the baby. Babies were exposed to 0.28% of the weight-normalized maternal dose which is considerably less than 10% level of concern. Another 2003 study, this time conducted by different researchers at the Christchurch Hospital in New Zealand, also found that infant exposure to metformin transmitted in breastmilk was low and that, because of such low exposure to the drug, metformin appears to be safe.

Additionally, a study published in the May 2006 issue of the Journal of Pediatrics examined the motor and social development of formula-fed infants, breastfed infants and breastfed infants of mothers treated with metformin. All mothers in the study suffered from PCOS. Researchers found no differences among the infants' growth, social or motor development, and they concluded that metformin treatment of PCOS mothers during lactation is both safe and effective.

Approaching Your Doctor
Certainly, some conservative doctors who are either unfamiliar with or wary of the current research on the subject of metformin and lactation, will not prescribe the drug to breastfeeding mothers despite its documented benefits for the mother and safety for both mother and child. This is not dissimilar to conservative obstetrician-gynecologists refusing to continue prescribing metformin for pregnant women with PCOS despite benefits such as reduced risk of miscarriage.

Again, a plan to treat PCOS should be designed for every individual and ought to include a risk/benefit analysis; however, the research on metformin during lactation appears to indicate it is safe for babies and effective for mothers.

If a mother feels confident that metformin is the appropriate treatment for her, she should contact her doctor about getting a prescription. Most doctors who are up-to-date on current research will have no qualms prescribing metformin for breastfeeding mothers; for those doctors who are hesitant in prescribing the drug, a mother might provide her doctor with copies of current research studies as well as a copy of Dr. Hale's Medications and Mothers' Milk. Mothers should also be empowered to seek out a second opinion.

For Further Study
Medications and Mothers Milk. Hale, Thomas. Hale Publishing, LP. May 2006.
Mother Food for Breastfeeding Mothers. Jacobson, Hillary. Pagefree Publishing. May 2004.
"Growth, motor, and social development in breast- and formula-fed infants of metformin-treated women with polycystic ovary syndrome." Glueck, Charles et al.
The Journal of Pediatrics: Volume 148, Issue 5. May 2006. Pages 628-632.
"Transfer of metformin into human milk." Hale, Thomas et al. Diabetologia: Volume 45, Number 11. November 2002. Pages 1509 - 1514.
"Transfer of metformin into human milk." Gardiner, Sharon et al. Clinical Pharmacology and Therapeutics: Volume 73, Issue 1. January 2003. Pages 71 - 77.