Nubain (nalbuphine) is just another opioid, similar to Stadol (butorphanol). The reason they usually offer these opiods, instead of something more potent (like morphine or fentanyl) is probably because Nubain and Stadol are a different class of opioids. They are partial agonists (morphine and fentanyl are pure agonists). Because of this, the amount of CNS and respiratory depression in both the mom and the baby are less. But their analgesic potency is less as well. And, when given in the face of excruciating pain, they will not do too much in controlling pain. For optimal pain control, thery should be given before the onset of pain. Obviously, this is not an option for laboring women.