neonatal abstinence syndrome (NAS), a behavioral pattern of irritability, tremulousness, and inconsolability exhibited in newborns exposed to heroin and methadone in the womb. The infant is born addicted to the drugs used by the mother. Symptoms of NAS are associated with withdrawal from those drugs. Following treatment during the neonatal period, the abnormal signs usually resolve. In some infants hypertonicity has persisted for 6 months. See also infant of chemically dependent mother.
