According to the U.K. National Health Service, paracetamol may be used safely by breastfeeding mothers. Though small amounts of the chemical will reach the baby via the breast milk, such doses are too small to cause any damage in healthy babies.
Drugs.com mentions that for a mother's dose of 1,000 milligrams of acetaminophen, the name paracetamol is known by in the United States, the baby will receive between 1 and 2 percent of the substance through breastfeeding. Though side effects are rare, there is a documented case of a breastfed infant who developed a rash two days after his mother took paracetamol and again after his mother took a new dose weeks later. It is recommended that breastfeeding mothers avoid taking this medicine in intravenous form.