Metformin and Breastfeeding
In clinical studies, metformin was shown to pass through breast milk in relatively low amounts. While many women are able to breastfeed and take metformin without any problems, it's still important to discuss your particular health situation with your healthcare provider. Extra caution needs to be taken in certain cases, such as with newborns and premature infants.
Metformin (Glucophage®) is passed through breast milk. It is recommended that healthcare providers look at the possible risks and benefits before recommending metformin while breastfeeding. Therefore, if you are breastfeeding or thinking of starting, make sure to let your healthcare provider know.
Data from well-conducted studies of metformin use during breastfeeding shows that levels of metformin in breast milk are relatively low and babies would receive less than 0.5 percent of their mother's dose. Although the level of metformin in the milk is low and is often undetectable in a baby's blood, sometimes low levels are found.
In a relatively large study that compared breastfed infants of women using metformin to formula-fed infants, no differences were found between the two groups in height, weight, motor or social development, or rates of illness. Also, the same relatively large study, as well as numerous smaller studies, observed no side effects in the nursing babies. Some studies even reported normal blood sugar levels in babies after breastfeeding.
With some medications, it is beneficial to try to time breastfeeding and medication use so that the baby does not feed during times when blood levels of the drug are likely to be high. However, timing of breastfeeding with respect to when a woman took her metformin dose was found to be of little benefit, because drug levels in the milk are fairly constant during its use.
Even though metformin levels in breast milk are low and no side effects have been observed in the babies, it is recommended that the drug still be used with caution while nursing, especially in newborns, premature infants, and those with kidney problems.