Breast feeding should be promoted with confidence unless active substance use is occurring or otherwise contraindicated. Breastfeeding may reduce the severity of neonatal withdrawal syndrome in the neonate. With Methadone about 1-3% of maternal dosage will be transferred into the breast milk and with buprenorphine the amount of buprenorphine in breast milk is <1 percent of maternal dose. There is a low oral bioavailability with significant absorption unlikely.
Neonatal abstinence syndrome (NAS) is a phenomena when the infant withdraws from drugs that they have been exposed to in utero. NAS is not unique to opioids and can occur with benzodiazepines, nicotine and also SSRI and SNRIs. Methadone causes a withdrawal syndrome in 60–80% of cases with symptoms occurring usually between 48 to 72 hours after birth but also up to five days. In rare circumstances symptoms can be delayed by up to a month. The severity of NAS is not related to the maternal dose of Methadone.
There are lower rate of NAS with buprenorphine compared to methadone which is thought to be secondary to: lower bioavailability, lower transplacental passage and partial agonism. The risk of NAS with buprenorphine is also not dose dependent. However overall the risks of opioid withdrawal during pregnancy are greater to the foetus than those of NAS to the infant so it is important to adequately treat the pregnant woman with opioid use disorder rather than be concerned about the risks of NAS.