A clinical trial to evaluate length of stay, growth velocity and clinical outcomes in infants with neonatal abstinence syndrome receiving an exclusive human milk diet. Human milk is defined as expressed human milk or donor milk and its derivatives, human milk-based fortifier and human milk caloric fortifier.

This is a single blinded (physician investigator), randomized, controlled trial to evaluate length of stay in infants with NAS and an exclusive human milk diet during their initial hospitalization after birth and through the 28 days of life or hospital discharge, whichever comes first.

Subjects will be randomized to one of two groups after at birth. Parents who decline participation for their infants in the study will be asked to consent to data gathering on their infants who will be treated and fed per institutional practice. The data on these individuals will be summarized and evaluated descriptively in comparison with the actual trial results.

All experimental group participants will receive exclusive maternal human milk or donor human milk prior to randomization. Once randomized, patients in Group One will receive an exclusive human milk diet throughout the 28-day feeding period or until hospital discharge, whichever comes first. Patients in Group Two (Control Group) will receive maternal human milk or formula (per standard of care). Fortification will be implemented with a standard protocol.

Inclusion Criteria:

1. Term infants (≥37 and 0/7 weeks gestational age) ≤ 2 days old with a diagnosis or at risk for neonatal abstinence syndrome. Can be enrolled ante-natally.
2. Infant feeding was NPO (nil per os) or consisted of 100% human milk diet prior to randomization.
3. Parent(s) willing to sign informed consent.
4. Parent(s) willing to comply with study follow-up procedures.

Exclusion Criteria:

1. Term infants >2 days old at the time of evaluation for NAS.

2. <37 weeks gestation.

3. Outborn infants who received enteral nutrition at the other institution prior to transfer. If it is uncertain if infant received even 1 bottle or a small amount of formula, infants will be excluded.

4. Major congenital abnormalities:

   1. Confirmed or suspected major genetic abnormalities (lethal or with extremely low probability for survival).
   2. Chromosomal abnormalities: Trisomies (13, 18, 21 etc.) deletions or translocations (Turner/Williams Syndrome, DiGeorge, to name a few).
   3. Major organ system abnormalities not related to a genetic syndrome that are lethal or have extremely low probability for survival (i.e, bilateral kidney intrinsic disease, pulmonary hypoplasia, CNS (central nervous system) malformations: Arnold Chiari, myelomengoceles, hydranencephaly, squizencephaly, holoprocencephaly).

5. Any comorbidity or significant clinical event prior to enrollment, deemed by the Investigator as likely to affect survival or intestinal health.

6. Legally Authorized Representative(s) unwilling to comply with an exclusive human milk diet either in the form of mother's milk, human milk-based human milk fortifier, human milk based caloric fortifier or donor human milk during the initial hospitalization period and through the 28 day feeding period or hospital discharge, whichever comes first.

Physician Investigator will be blinded