In a study of one nursing mother taking three tablets of St. John's Wort per day (Klier 2002), the levels of various components of the herb in breastmilk ranged from low to below the detection limits. No side effects were observed in the mother or infant.
Thomas Hale, RPh, PhD, author of Medications and Mothers' Milk, says that St. John's Wort appears to be relatively safe for nursing mothers, but recommends that caution be used. He suggests that other treatments (Zoloft, Paxil) are probably preferred.
Herbals and Breastfeeding (Nice 2000) says that no known contraindication to breastfeeding exists, but suggests that the nursling be monitored for potential side effects.
Ruth Lawrence, MD, in Herbs and Breastfeeding says that breastfeeding mothers should not take St. John?s Wort without consulting their physician first.
Herb expert Tieraona Low Dog, MD, in PDF Herbal Medicine - An Evidence-Based Approach does not list breastfeeding as a contraindication to taking St. John's Wort.
A Review of 12 Commonly Used Medicinal Herbs (O'Hara 1998), does not warn against its use during lactation, but says that it should not be used during pregnancy (uterotonic) or with other psychoactive agents. St. John's Wort can cause photosensitivity, especially in fair-skinned persons taking large doses.