Because there is no currently approved treatment for postpartum depression, what they’re comparing here is the danger of untreated PPD against the danger of either discontinuing breastfeeding or having the newborn ingest a small amount of this medication. Untreated PPD is no joke. Not only does the mother’s suffering matter in itself, it has serious documented effects on the baby.
And there is nothing wrong or negligent about “solving this with a pill.” It needs solving. It is a serious issue.