Naltrexone Use in Pregnancy
Primary Recommendation
Naltrexone should not be initiated during pregnancy for opioid use disorder (OUD), but may be continued in women already taking it after careful risk-benefit assessment and informed consent. 1, 2
Evidence-Based Guidance
For Women Not Currently on Naltrexone
Do not start naltrexone during pregnancy - The Society for Maternal-Fetal Medicine, ACOG, and American Society of Addiction Medicine joint workshop explicitly states that "data are insufficient to support the initiation of naltrexone therapy during pregnancy." 1
Offer methadone or buprenorphine instead - All pregnant women with OUD should be offered maintenance therapy with methadone or buprenorphine, which are the only medications considered safe throughout all trimesters for OUD treatment. 1, 3
For Women Already Taking Naltrexone Who Become Pregnant
Continuation may be considered after weighing the risk of relapse (if discontinued) against the limitations of pregnancy safety data. 1, 2
Informed consent is mandatory - Patients must acknowledge the lack of pregnancy safety data before continuing naltrexone. 2
First trimester exposure should be minimized when possible, as this is the period of organogenesis. 2
FDA Pregnancy Classification and Animal Data
Pregnancy Category C - The FDA label indicates naltrexone increased early fetal loss in rats at doses ≥30 mg/kg/day (5 times the recommended human dose) and in rabbits at ≥60 mg/kg/day (18 times the recommended human dose). 4
No evidence of teratogenicity was found in animal studies at doses up to 200 mg/kg/day during organogenesis. 4
Naltrexone is excreted in rat milk, and it is unknown whether it is excreted in human milk; caution is advised during breastfeeding. 4
Emerging Research Context
Recent small-scale studies provide limited reassuring data:
A 2024 case series of 7 pregnant individuals treated with naltrexone showed no return to nonprescribed opioid use, no fetal anomalies, no neonatal opioid withdrawal syndrome, and one preterm delivery. 5
A 2017 retrospective cohort found higher pregnancy loss rates in naltrexone-treated women compared to buprenorphine and controls, but higher birth rates overall compared to all groups. 6
These studies are too small and of insufficient quality to change guideline recommendations. 7, 8
Critical Pitfalls to Avoid
Do not extrapolate standard-dose naltrexone data to low-dose formulations without acknowledging this limitation. 2
Do not withhold methadone or buprenorphine in favor of naltrexone - these are the evidence-based first-line treatments with established safety profiles. 1, 3
Do not attempt detoxification to initiate naltrexone during pregnancy - the opioid-free period required for naltrexone induction creates vulnerability for relapse, increased risk behaviors, and potential overdose. 7, 8
Special Considerations for Alcohol Use Disorder
For pregnant women with alcohol use disorder (AUD), a 2021 review suggests naltrexone "should be considered" given the substantial risks of alcohol consumption during pregnancy, though more research is warranted. 9
The risk-benefit calculation differs for AUD versus OUD, as there are no established medication alternatives for AUD comparable to methadone/buprenorphine for OUD. 9
Obesity Management Context
- Naltrexone-bupropion combination (used for obesity) should not be used during pregnancy or lactation, and women of reproductive age should use effective contraception. 1