Compatible: Drug which has been taken by a large number of breastfeeding mothers without any observed increase in adverse effects in the infant. Controlled studies in breastfeeding women fail to demonstrate a risk to the infant and the possibility of harm to the breastfeeding infant is remote; or the product is not orally bioavailable in an infant.
Probably Compatible: Drug which has been studied in a limited number of breastfeeding women without an increase in adverse effects in the infant. And/or, the evidence of a demonstrated risk which is likely to follow use of this medication in a breastfeeding woman is remote.
Probably Compatible: There are no controlled studies in breastfeeding women, however the risk of untoward effects to a breastfed infant is possible; or, controlled studies show only minimal non-threatening adverse effects. Drugs should be given only if the potential benefit justifies the potential risk to the infant. (New medications that have absolutely no published data are automatically categorized in this category, regardless of how safe they may be.)
Possibly Hazardous: There is positive evidence of risk to a breastfed infant or to breastmilk production, but the benefits of use in breastfeeding mothers may be acceptable despite the risk to the infant (e.g. if the drug is needed in a life-threatening situation or for a serious disease for which safer drugs cannot be used or are ineffective).
Hazardous: Studies in breastfeeding mothers have demonstrated that there is significant and documented risk to the infant based on human experience, or it is a medication that has a high risk of causing significant damage to an infant. The risk of using the drug in breastfeeding women clearly outweighs any possible benefit from breastfeeding. The drug is contraindicated in women who are breastfeeding an infant.
3. Hale, T. W. (2002). Medications in Mother’s Milk (10th edition). Amarillo, TX: Hale Publishing.
BREASTFEEDING DRUG RISK DEFINITIONS OF RECOMMENDATIONS
Either the drug is not excreted in clinically significant amounts into human breast milk or its use during lactation does not, or is not expected to, cause toxicity in a nursing infant.
The drug may or may not be excreted into human breast milk, but the maternal benefit of therapy far outweighs the benefits of breast milk to an infant. Breastfeeding should be held until maternal therapy is completed and the drug has been eliminated (or reaches a low concentration) from her system.
NO (LIMITED) HUMAN DATA – PROBABLY COMPATIBLE
Either there is no human data or the human data are limited. The available data suggest that the drug does not represent a significant risk to a nursing infant.
NO (LIMITED) HUMAN DATA – POTENTIAL TOXICITY
Either there is no human data or the human data are limited. The characteristics of the drug suggest that it could represent a clinically significant risk to a nursing infant. Breastfeeding is not recommended.
HUMAN DATA SUGGEST POTENTIAL TOXICITY
Human data suggest a risk to a nursing infant. The drug is best avoided during breastfeeding. Depending on the drug short-term use by the mother may be possible, but the infant should be closely monitored for potential adverse effects.
NO (LIMITED) HUMAN DATA – POTENTIAL TOXICITY (MOTHER)
Either there is no human data or the human data are limited. The characteristics of the drug suggest that breastfeeding could represent a clinically significant risk to the mother such as further loss of essential vitamins or nutrients. Breastfeeding is not recommended.
There may or may not be human experience, but the combined data suggest that the drug may cause severe toxicity in a nursing infant, or breastfeeding is contraindicated because of the maternal condition for which the drug is indicated. Women should not breastfeed if they are taking the drug or have the condition.
 Briggs, Gerald G., Freeman, Roger K. (2015) Drugs in Pregnancy and Lactation Tenth Edition.