Use of addicting drugs among women during pregnancy exposes newborns to potentially serious disorders. A group of symptoms referred to as neonatal withdrawal syndrome (NWS) may occur in infants born to mothers addicted to certain drugs because, at birth, the infants suddenly are cut off from the drug supply. Classes of drugs that cause NWS are those that produce addiction in adults, including the opioids (heroin, methadone, morphine), barbiturates, alcohol, and benzodiazepines. Many of the manifestations of NWS occur regardless of the class of drug, including irritability, hyperactivity, abnormal sleep pattern, high-pitched cry, tremor, vomiting, diarrhea, weight loss, and failure to gain weight. The fact that these symptoms are nonspecific makes it difficult to identify NWS unless it is specifically looked for. The onset, duration, and severity of the disorder differ based on such factors as the addictive drug used, time and amount of mother's last dose, and rate of elimination of the drug from the newborn. Pharmacologic intervention may be required to control severe symptoms and signs. The most common drugs used to modify withdrawal are phenobarbital, paregoric, chlorpromazine, and diazepam. Treatment is complicated by conflicting information on the effectiveness of various agents.