Neonatal Abstinence Syndrome (NAS) is a set of neurobehavioral features observed in newborns who have been exposed to drugs such as opioids, benzodiazepines, and selective serotonin reuptake inhibitors during pregnancy. This condition is documented in the NCI Thesaurus under the code C87101.Neonatal Abstinence Syndrome (NAS) is a set of neurobehavioral features observed in newborns who have been exposed to drugs such as opioids, benzodiazepines, and selective serotonin reuptake inhibitors during pregnancy. This condition is documented in the NCI Thesaurus under the code C87101.