Pam:  Although this has not (yet) been demonstrated in scientific studies,
there is a plausible physiologic reason to assume that breastfeeding could
reduce symptoms of endometriosis.  Although combination OC's are sometimes
useful in mild endometriosis (probably because they suppress ovulation),
for more severe cases, drugs such as danazol (danocrine) and lupron are
effective.  These drugs are anti-estrogenic in their effects.
Breastfeeding both inhibits ovulatory cycles (therefore should
theoretically be as effective as the combination OC's the physician wants
to prescribe, especially for the duration of lactational amenorrhea), and
reduces estrogen levels (therefore should have some of the effects of the
anti-estrogenic drugs).
This physiologic reasoning would provide an understanding of the many
anecdotal reports from mothers with endometriosis who state that their
symptoms decreased while breastfeeding.  Hopefully, there will soon be an
actual study confirming this phenomenon.  In the meantime, I see little
justification for weaning in order to take OC's for their anovulatory
effect.  If this were my patient, I would encourage her to nurse in the
ecological, LAM, way (i.e. fully "on demand" with no supplements, no
pacifiers, with night feedings, avoidance of early solid introduction,
etc) for at least 6 months.  If this weren't possible for her due to work,
then I would recommend frequent pumping while away from baby and
ecological type of breastfeeding when together with baby.  This is at
least as likely to help keep her endometriosis at bay as taking OC's, and
she and the baby would derive all the other benefits of breastfeeding as
well.  If her symptoms were to recur at any time in the future, then
medications for her endometriosis could be reconsidered.
Hope this helps, Alicia Dermer, MD, IBCLC.