In my experience acetaminophen has little or no effect on this type of sore nipples because it is not an anti-inflamitory. It also passes thru the milk and has a sig half life. 4.2 nanograms/ml 2 hrs post dose of 500mg. Acetaminophen is liver toxic. I worry about the cumulitive effects in both mother and baby, especially with a baby's immature liver Mother may have a neuritis from the constant irritation. Ibuphrofen is an anti-inflamitory and will calm down the irritated nerves. Briggs states that ibuprofen does not enter the milk in sig. quantities: less than 0.5 nanograms/ml. It is not hepatotoxic. And may be a better choice. On a side note: many of our midwives switched from acetaminophen to ibuprofen because the latter worked so well with afterbirth pains.