Morphine for a newborn..why?

i know a baby who's in the same nicu as my son was, i talked to the parents when we saw each other but never felt comfortable asking..the baby was born 2 weeks early a little over 5 pounds, appeared fine physically, but was being given the minimum dose of morphine regularly, i was wondering why they would do this, baby is now 5 weeks old and still in the nicu, as i was there yesterday donating the preemie clothes that my son outgrew