Blood into breastmilk and breastmilk into blood.  This is a two way street,
and with the exception of a few drugs, as the blood levels decline, the
drugs will return into the blood and the milk level will decrease.  Even the
drugs which are most highly trapped in the milk (iodine, for instance),
eventually will work their way back into the blood, albeit very slowly, if
the maternal blood level does not continue to furnish more drug.

There is no need to stop for the vast majority of drugs.

Jack Newman, MD, FRCPC