While it is commonly known that many medications cannot be taken while pregnant, mothers are often left wondering what is safe to take while they are breastfeeding their baby.  The good news is that most medications are compatible with breastfeeding.  

Unfortunately, many mothers are given inaccurate advice with regard to medications and breastfeeding or avoid taking essential medications because of fear of adverse effects on their infants.  

Virtually all medicines are excreted to some extent into breast milk.  Very few pose any concern to an infant.  The amount transferred into breast milk is usually very small and unlikely to affect your baby. 

What determines how much medication gets into breast milk?

Medications transfer into breast milk in varying amounts depending on several factors.  These include:

  • Maternal plasma concentration
    • Higher amounts of drug in the mother can mean higher amounts present in breast milk. 
    • This is affected by which tissues the drug distributes to in the mother’s body. A high volume of distribution means less drug in the breast milk. 
  • Maternal plasma protein binding
    • Some drugs attach themselves to proteins found in the blood.  The more a medication attaches to proteins in the mother’s blood, the less drug is available to transfer into breast milk.
  • Size of the drug molecule
    • Larger drug molecules are less able to transfer into breast milk.
  • Degree of ionisation
    • Drugs cross membranes only in unionised form – this means that certain medications cannot cross the membranes into breast milk.
  • Fat solubility
    • Some drugs dissolve into fat more readily that others.
  • Maternal genetics
    • How a mother metabolizes a medication can affect how much drug gets into breast milk. 

Minimizing Risk to Nursing Infants

There are some considerations given when prescribers are choosing which medication can be given to a nursing mother to avoid any potential risk to the infant.  There are very few reasons why medications essential to the mother’s health and well-being need to be avoided.  

Based on the above factors determining how much medication is present in breast milk, prescribers should choose medications that are short acting, are more protein bound, have low fat solubility, and have been studied in infants.  These medications are not present in breast milk is any considerable amount and pose minimal risk. 

If a medication that the nursing mother is prescribed can be given directly to an infant for a medical condition, then that medication would be generally considered safe while breastfeeding.  This is because the amount of medication in breast milk is significantly less than what would be given if actually prescribed to an infant.  

If a medication is meant to be taken once a day, infant medication exposure can be minimized if the medication is taken just after nursing before the infants longest stretch of sleep (i.e. just after bedtime feeding). 

Some medications affect how much breast milk is produced.  Examples of medication that increase breast milk supply include domperidone or metoclopramide.  Medications that adversely affect breast milk supply include estrogen containing oral contraceptives, nicotine, and decongestants.  

Talk to your Pharmacist or Doctor

Before taking any over-the-counter or prescription medications, talk to your pharmacist or doctor.  They can review up to date information with regard to infant safety during maternal consumption of medications during breastfeeding.  

Some useful links are available on the internet:

Infant Risk Center

Drugs and Lactation Database

This post was co-authored by Erin Manchuk, BScPharm, BCGP and Stephanie Liu, MD, MSc, CCFP, BHSc.