Notably, one report showed that high methylation of three specific CpG sites of the OPRM1 promoter is associated to a worse NAS outcome in newborn babies from mothers receiving methadone or buprenorphine during pregnancy, likely due to the subsequent lower expression of the receptor and a need for higher doses of opioid medication to control NAS symptoms (Wachman et al., 2014). Here, OPRM1 is linked to neonatal abstinence syndrome.