They give peppermint after a c-section, if you have trapped wind, which sounds mild, but beleive me, is INCREDIBLY painful - so much so that when someone suggested it was only wind, I scoffed with indignation.
But once I was given peppermint, the pain totally went away.
Multiple doses are thus not required.
IF it is true, that it reduces supply, really that shouldn't be an issue, because if you do need it for pain, you would only need a single dose, anyway, so this is not really going to effect supply.