Limited data indicate that naltrexone is minimally excreted into breastmilk. If naltrexone is required by the mother, it is not a reason to discontinue breastfeeding.
Naltrexone is used as maintenance treatment of opiate dependence in opiate-detoxified patients. Peak plasma levels of 40 to 50 mcg/L at 1 hour after the dose and average plasma levels of 3 to 5 mcg/L have been reported in adults taking daily maintenance doses. Oral bioavailability is 5 to 40% in adults. Naltrexone is metabolized to active beta-naltrexol and to other inactive metabolites.
One lactating woman who was 1.5 months postpartum and taking 50 mg of oral naltrexone daily during pregnancy and lactation had her milk sampled several times between 3.7 and 23 hours after her dose. Naltrexone milk levels were undetectable (<2 mcg/L) by 8 hours after the dose while beta-naltrexol milk levels remained detectable throughout the study period and averaged 46 mcg/L. The half-life of elimination from milk was 2.5 and 7.7 hours for naltrexone and beta-naltrexol, respectively. The authors reported that an exclusively breastfed infant would receive about 7 mcg/kg daily of naltrexone including the active metabolite, equivalent to 0.86% of the maternal weight-adjusted dosage.
A 1.5 month-old breastfed male infant of a mother who was taking 50 mg of oral naltrexone daily during pregnancy and lactation had undetectable (<2 mcg/L) plasma levels of both naltrexone and beta-naltrexol 9.5 hours after the maternal dose, 30 minutes after starting a feeding.
Effects in Breastfed Infants:
A 1.5-month-old breastfed infant of a mother who was taking 50 mg of oral naltrexone daily during pregnancy and lactation was reportedly healthy with no naltrexone-related adverse effects.
Possible Effects on Lactation:
Relevant published information was not found as of the revision date.
1. Chan CF, Page-Sharp M, Kristensen JH et al. Transfer of naltrexone and its metabolite 6,beta-naltrexol into human milk. J Hum Lact . 2004;20:322-6. PMID:15296587
CAS Registry Number:
LactMed Record Number:
Last Revision Date:
Disclaimer:Information presented in this database is not meant as a substitute for professional judgment. You should consult your healthcare provider for breastfeeding advice related to your particular situation. The U.S. government does not warrant or assume any liability or responsibility for the accuracy or completeness of the information on this Site.