Phase 1 is a randomized, controlled, double-blinded study comparing the use of low-dose ketamine (LDK) to morphine for acute pain control in emergency department patients. A convenience sample of subjects will be enrolled from a population of patients aged 18-50 who present to the Brooke Army Medical Center Emergency Department with acute abdominal pain, flank/lumbar back pain and/or pain to the extremities. To take part in the study, a need for opioid analgesia must be indicated by the treating physician in addition to the patient meeting all other study criteria.