Prevacid, according to Dr Hale's book, like it's sister proton pump inhibitor,
Prilosec, is generally not recommended in breast feeding mothers though it's
probably OK.  Pepcid (a weaker acid suppressing medicine from the H-2 Blocker
class of anti ulcer medicines) is a preferable choice if she hasn't already
failed treatment with it. If she has failed treatment with an H-2 Blocker such
as pepcid then higher doses of the pepcid in addition to dietary changes such
as no alcohol, citrus juices, non-steroidals, late night meals, smoking,
chocolate, etc will also help.  Antacids are also very safe and can be used in
conjunction with the pepcid.

Peter Salomon, MD FACG