OBJECTIVES:  Pregnant women may use promethazine or ondansetron for nausea and vomiting during pregnancy (NVP).   The long-term safety and its potential risks on the fetus and newborns are widely unknown. Promethazine has a black boxing warning for contraindicating its use in infants and young children. The purpose of this study was to quantify and describe adverse events (AEs) related to these two medications in child-bearing age women and young children.  METHODS:   The data source was the FDA’s Adverse Events Reporting System database from 1997 to 2006.  Using a retrospective data analysis, AEs for all patients with study drugs were compared to that for children ages 0-6 years old and women of child-bearing age (CBA) 15- 50 years old.  The annual frequencies of AEs for both study drugs were analyzed and stratified by age group and gender.  The related AEs were categorized by clinical outcomes, pregnancy outcomes, route of administration, and duration of therapy.  RESULTS: A total of 392,229 AEs for promethazine and 282,056 AEs for ondansetron were reported.  Of those, 13.7% of ondansetron and 22% promethazine AEs were for CBA women with the peak for age 35-50; while 13.1% ondansetron and 13.8% promethazine AEs were for children age 0-6 with the peak for age 0-2.    There were 23.68% and 13.54% AEs related to promethazine and ondansetron long-term use (greater than 90 days) among CBA women, respectively.  The most common routes of administration were oral and intravenous.  For CBA women, the frequent AE pregnancy outcomes were maternal complications (26%), premature labor (9%), maternal drugs affecting fetus (8%) and spontaneous abortion (4%); while the most frequent AEs for children were neonatal respiratory arrest (0.25%) and neonatal apneic attack (0.17%).  CONCLUSIONS: AEs of promethazine and ondansetron among children and CBA women are common.  The risk of their off-label use for the long-term treatment of NVP should be recommended with cautions.