I would concur with Dr. Newmans' prior "musings".  Transplacental transfer of
drugs is significantly different (and generally more) when compared to the
transfer of drugs in human milk.  It appears far more difficult for drugs to
enter milk than enter the fetus.  It is apparent to me that the transfer of
drugs into milk is about as difficult as the transfer through the Blood-Brain
barrier,  and most drugs have great difficulty in passing both of these
barriers.

I would surmise that nature provided this "safety factor" to protect the human
infant (postpartum) from exogenous substances that mom may ingest.  Isn't
nature wonderful.

Regards
Tom Hale,PH.D.