Hale's Breastfeeding Safety Ratings: Part 1 - Rating System

Thomas Hale’s Medications and Mothers’ Milk, now in its fourteenth edition, has become the standard reference for the breastfeeding safety of medications.  In this series, we will provide a summary of Dr. Hale’s ratings and recommendations for the major classes of psychiatric medications.  In this first entry in the series, we present the key components of Dr. Hale’s lactation safety rating system. 

One estimate of risk is provided by the level of exposure for a nursing infant.  Dr. Hale reports the Relative Infant Dose (RID) for each medication as an index of the level of exposure.  Expressed as a percentage, the RID is calculated by dividing the infant’s total daily ingestion of a medication via nursing (expressed as mg per kg infant body weight) by the mother’s daily dose of the medication (expressed as mg per kg maternal body weight).  Dr. Hale advises that “a Relative Infant Dose of <10% is considered safe”, though we would caution that this is a general observation that has never been objectively verified.  Earlier studies had utilized milk:plasma ratio as an index of the level of exposure, but it has been abandoned in favor of RID in recent years.  We agree with Dr. Hale that “the milk:plasma ratio is virtually worthless” because it does not provide an estimate of the total amount of a drug that is transferred to a nursing baby.

Dr. Hale’s Lactation Risk Categories include:

L1 SAFEST – Drug has been taken by many breastfeeding women without evidence of adverse effects in nursing infants OR controlled studies have failed to show evidence of risk.

L2 SAFER – Drug has been studied in a limited number of breastfeeding women without evidence of adverse effects in nursing infants.

L3 MODERATELY SAFE – Studies in breastfeeding have shown evidence for mild non-threatening adverse effects OR there are no studies in breastfeeding for a drug with possible adverse effects.

L4 POSSIBLY HAZARDOUS – Studies have shown evidence for risk to a nursing infant, but in some circumstances the drug may be used during breastfeeding.

L5 CONTRAINDICATED – Studies have shown significant risk to nursing infants.  The drug should NOT be used during breastfeeding.

D.J. Newport M.D.