Publication Details

Estimated reading time: 1 minute

CASRN: 16590-41-3

SID: 134993601

Drug Levels and Effects

Summary of Use during Lactation

Limited data indicate that naltrexone is minimally excreted into breastmilk. If the mother requires naltrexone, it is not a reason to discontinue breastfeeding.[1]

Drug Levels

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.

Maternal Levels. 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-lives of elimination from milk were 2.5 and 7.7 hours for naltrexone and beta-naltrexol, respectively. The authors estimated 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.[2]

Infant Levels. 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.[2]

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.[2]

Effects on Lactation and Breastmilk

Relevant published information was not found as of the revision date.

Alternate Drugs to Consider

Buprenorphine, Methadone


Harris M, Schiff DM, Saia K, et al. Academy of Breastfeeding Medicine Clinical Protocol #21: Breastfeeding in the setting of substance use and substance use disorder (Revised 2023). Breastfeed Med 2023;18:715-733. [PubMed: 37856658]
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. [PubMed: 15296587]

Substance Identification

Substance Name


CAS Registry Number


Drug Class

Breast Feeding


Milk, Human

Alcohol Deterrents

Narcotic Antagonists

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