The primary hypothesis to be tested in this double blind, randomized controlled trial is that Nalbuphine is equivalent to morphine for pain control and patients will suffer fewer episodes of acute chest syndrome. The investigators also expect subjects will report fewer side effects from respiratory depression, abdominal distention from reduced peristalsis, reduced histamine release causing pruritis and still be provided adequate pain control. Further hypotheses to be tested is ability to recruit patient participants while being treated in the Emergency Department and that continuous infusion of Nalbuphine with accompanying patient controlled analgesia (PCA) is safe and effective in controlling pain, requiring less total opiates consumption, while decreasing length of hospitalization.