This has been discussed many times in this forum, and should be in the
archives.

The combined pill often decreases milk supply.  It should be avoided
at any time in nursing mothers.  The progestin only pill is not
supposed to decrease milk supply, but some observers feels that it
might.  There might be an insignificant increase in the hormones
reaching the baby, but this is extremely unlikely to have any
significant effect for the baby.

Birth control should be explored in depth with any woman so that she
can decide what is best in her case.  The reason the pill is
"preferred" by so many hcp's is that it is so easy to write a
prescription without going through the counselling part of it.  The
pill *might* be best for a particular woman, but often is not,
especially for breastfeeding women.  The lactation amenorrhea method
is rarely ever mentioned by physicians because they don't know about
it, or don't believe it works, or just do not trust anything which
does not include control by someone other than the woman herself.

Jack Newman, MD, FRCPC