Venafaxine is excreted into breast milk.  Infant levels as high as 9% of
maternal levels have been detected.  Although no adverse effects have been noted
in infants, infants should be monitored for agitation, insomnia, and poor
feeding.
Use alternative SSRI if possible, eg, paoxetine (Paxil), sertraline (Zoloft), or
even fluoxetine (Prozac).

Frank J. Nice, DPA, CPHP