Hi Alison,
Yes, I see this from time to time, even in moms who pump at work and have a
very good knowledge of their supply.  The drop, if it occurs, happens within
a week and might or might not bounce back with continued pumping.  Stopping
the pill usually brings the supply back up.  Since progesterone inhibits
prolactin and prolactin's effect diminishes over time, I'd expect to see less
of a response if mom waits 3+ monts before trying.  I've seen the same with
Nor... implanted contraceptives.  Interesting that the manufacturer of one
brand also makes artificial baby milk.

Linda Smith, BSE, FACCE, IBCLC
Dayton OH