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QUESTO HEALTHCARE ECOSYSTEM Clinical Pharmacology & Maternal-Fetal Drug Safety Center

Document ID: Q-PREG-D38C22E8

Date Issued: October 07, 2026

Regulatory Base: US FDA (PLLR 8.1/8.2) & NIH LactMed®

Verified Portal: questocomm.com/pregnancy-safety/ondansetron

OFFICIAL CLINICAL MONOGRAPH

ONDANSETRON

Evidence-Based Medication Safety Profile for Maternal & Lactation Practice

Pregnancy & Lactation Center

Clinical Monograph 5-HT3 Receptor Antagonist Antiemetic

Human Data Available

Ondansetron

UNII Code 4AF302ESOS

CAS Registry 99614-02-5

RxNorm CUI 26225

Historical FDA Category B

Prescribing & Clinical Reference: Compiled from official regulatory labeling (US FDA PLLR, NIH LactMed®, EMA). Clinical decisions during pregnancy and lactation require individualized patient assessment and physician consultation.

1. Pregnancy Evidence & Regulatory Labeling

FDA Pregnancy and Lactation Labeling Rule (PLLR 8.1) & EMA SmPC Section 4.6

Clinical Risk Summary

Ondansetron is a commonly prescribed second-line antiemetic for refractory nausea and vomiting of pregnancy (NVP) and hyperemesis gravidarum (HG). Large cohort studies involving hundreds of thousands of pregnant women indicate that the baseline risk of major congenital malformations is not significantly increased. A very small possible absolute risk increase for oral clefts (~3 additional cases per 10,000 exposed) has been reported in some studies, but overall evidence supports favorable benefit-risk in severe maternal dehydration.

Human Pregnancy Experience & Clinical Studies

CDC and European database analyses of >1.8 million pregnancies demonstrate no overall increase in major structural defects.

Animal Reproductive & Developmental Toxicity Data

Reproduction studies in pregnant rats and rabbits revealed no teratogenicity at doses up to 6 times human exposure.

Clinical Considerations for Prescribers

ACOG guidelines recommend Vitamin B6 (pyridoxine) + Doxylamine as first-line therapy. Ondansetron is reserved for moderate-to-severe symptoms when initial therapies fail.

Placental Transfer

Crosses the placental barrier in early and late pregnancy.

2. Lactation & Breastfeeding Safety

NIH / NLM LactMed® Database & FDA Labeling Section 8.2

Summary of Use during Lactation

Limited published human data; however, excretion into human milk is estimated to be low. Short-term use for postpartum nausea is considered compatible with breastfeeding.

Drug Levels in Breast Milk & Relative Infant Dose

Relative Infant Dose (RID) Estimated <1.5% RID <10% is generally considered low by clinical guidelines.

Milk Concentration & Transport

Excreted in animal milk; small human case series show low milk concentrations.

Effects in Breastfed Infants & Monitored Signs

No adverse clinical events reported in breastfed infants.

Effects on Lactation & Milk Production

No known effect on prolactin or milk supply.

Alternate Medications with Established Lactation Data

Metoclopramide Doxylamine + Pyridoxine

4. Regulatory Source Provenance & Comparison

Direct attribution to official regulatory documents without synthesized consensus

Regulatory Organization	Jurisdiction	Document / Framework	Effective Date	Official Source Link
National Institutes of Health (NIH) / NLM LactMed® Database (Drugs and Lactation)	United States / Global	evidence_monograph	2026-08-01	Official Record

National Institutes of Health (NIH) / NLM LactMed® Database (Drugs and Lactation)

United States / Global

Framework: evidence_monograph

Effective Date: 2026-08-01

View Official Regulatory Record

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OFFICIAL CLINICAL NOTICE: This monograph is compiled from official U.S. FDA Prescribing Information (PLLR 21 CFR 201.57 Section 8), NIH / NLM LactMed®, and EMA Summary of Product Characteristics (SmPC 4.6). This document is intended solely for reference by licensed healthcare professionals and does not supersede individualized clinical judgment.