Do you need to wean?  Almost certainly not!  Our culture assumes that your choices are 1) known risk to your baby from continued breastfeeding or 2) no risk from consuming a safe formula.  Wrong!  There is no safe formula.  A single bottle of formula raises the risk of food sensitivities and allergies, increases the risk of illness for an unknown length of time, increases a susceptible baby's risk of diabetes, and disrupts the baby's intestinal activity for up to a month.  The real choices are usually 1) slight theoretical risk from a very small dose of the medication or 2) known risk from formula. 

     The vast majority of the time, "playing it safe" means continuing to breastfeed, not weaning.  Here are some of the reasons why:

*    Even if a mother's blood level for a given drug is high, it's still very dilute from the perspective of the breastfeeding baby.  Milk is made from the mother's blood.  Imagine trying to treat someone by providing not the drug itself but a dose of blood from someone else who has taken the drug! 

*    Any drug in the mother's milk is swallowed by the baby, and must pass through his digestive system before entering his own plasma.  Drugs that can be measured in the mother's blood and milk are often undetectable by the time they reach the baby's blood, or are present in barely measurable amounts.  And drugs that are given by injection because they're ineffective orally are usually just as ineffective when the baby swallows them in the milk.

*    Age matters.  Some drugs that might be a concern for premature infants are not a concern for full-term babies.  Some that are a concern for newborns are not a concern after the first month.  The older the baby, the more mature his systems.  And any baby who is also eating solids automatically gets less through his mother's milk. 

*    When in doubt, the baby's condition can be monitored, either by taking blood samples or just by watching for diarrhea or fussiness. 

*    Temporary weaning - and pumping, and dealing with bottle-feeding and an unhappy baby - is a big stress for an already stressed sick mother and her baby. 

*    Temporary interruption of breastfeeding can lead to early weaning.  Breastfeeding is a physiological relationship, not a faucet.  Turning it off abruptly is extremely disruptive to both mother and baby. 

*    The 2005 American Academy of Pediatrics statement on breastfeeding and the use of human milk has a very short list of medications that are contraindicated during breastfeeding, and even that list has exceptions.

*    Even with the few truly questionable drugs, there is usually "wiggle room" - nursing half-time, nursing "around the drug's peak time", waiting five half-lives, finding a safer alternate drug, and more. 

     If someone says you must wean, even briefly, talk with an International Board Certified Lactation Consultant, consult Thomas Hale's book, "Medications and Mothers' Milk", or check his website.  You'll like what you learn.