Background: We examined the safety of St. John's wort to nursing mothers and their infants.
Method: A prospective, observational, cohort study was conducted. Thirty-three breastfeeding women receiving St. John's wort (Group 1) who contacted our teratogen/toxicant counseling service regarding the safety of St. John's wort during breastfeeding were followed up between May 1999 and April 2001. These women were compared with 101 disease-matched (Group 2) and 33 age- and parity-matched nondisease controls (Group 3). Information collected included maternal and neonatal demographics, breastfeeding duration, use of St. John's wort, maternal and infant adverse events, infant weight over the first year of life, and whether or not the mother experienced a decrease in lactation.
Results: There were no statistically significant differences found in maternal or infant demographics or maternal adverse events. Whereas only 1 infant each in Groups 2 and 3 was reported to be colicky, there were 2 cases of "colic," 2 of "drowsiness," and 1 of "lethargy" in Group 1 (p <.01; Group 1 vs. Group 2, p <.01; Group 1 vs. Group 3, p =.20). Although 3 of these women in Group 1 consulted their doctor, specific medical treatment was not required. No significant difference was observed in the frequency of maternal report of decreased milk production among the groups, nor was a difference found in infant weight over the first year of life.
Conclusion: These results provide a framework for the management of breastfeeding women receiving St. John's wort.