Naltrexone During Pregnancy and Breastfeeding: What We Know

Key takeaways

• The old phrase “FDA Pregnancy Category C” is obsolete and should not drive a decision.
• Product labels say available human pregnancy data are insufficient to identify a drug-associated risk.
• Starting naltrexone requires an opioid-free interval; that is a major clinical consideration in opioid use disorder.
• LactMed calculated a total relative infant dose of 0.86% from one case, including naltrexone and its active metabolite.
• Continuing, stopping, or starting treatment should be decided with obstetric and addiction specialists after weighing medication uncertainty against the risks of untreated alcohol or opioid use disorder.

Why the old Category C wording is misleading

The FDA’s Pregnancy and Lactation Labeling Rule replaced letter categories because a single letter compressed very different evidence and clinical situations into an over-simple signal. Current US labels use narrative sections covering risk summary, clinical considerations, and data.

Older articles and labels may still quote Category C. That wording is historical, not the current FDA system.

What pregnancy evidence can—and cannot—show

Published human evidence consists largely of small observational cohorts and case reports, often involving people already stable on naltrexone. These records can identify reassuring signals, but they are not large enough to rule out uncommon outcomes or prove equivalence with other treatment choices.

Treatment context matters. The consequences of relapse, overdose, heavy alcohol exposure, destabilising an established treatment, or precipitating withdrawal can be serious. This is why a blanket “safe” or “unsafe” label is not useful.

What LactMed says about breastfeeding

The US National Library of Medicine’s LactMed review, revised in 2026, describes minimal excretion into breastmilk. In one case, estimated infant exposure to naltrexone plus 6-beta-naltrexol was 0.86% of the maternal weight-adjusted dose.

That is a reassuring pharmacokinetic observation, not proof from a large infant-safety study. Infant age, prematurity, feeding pattern, maternal dose, formulation, and other medicines can change the assessment.

Questions for the clinical team

1. Is the person already stable on oral or extended-release naltrexone, or considering initiation?
2. Is the indication alcohol use disorder or opioid use disorder?
3. What are the relapse, overdose, withdrawal, and alcohol-exposure risks of each option?
4. Which formulation and dose are involved?
5. What maternal, fetal, or infant monitoring is appropriate?

Primary sources

1. 01
   FDA: Pregnancy and Lactation Labeling Rule questions and answers
2. 02
   LactMed: Naltrexone

   Revised 2026; includes the single-case milk-transfer estimate.

3. 03
   FDA Vivitrol prescribing information, revised December 2025 (PDF)

   Narrative pregnancy and lactation sections.