Pain is a very common complaint in the emergency department (ED). The use of opioids to treat moderate to severe pain has increased over the last decade as well as the number of opioid related deaths. In 1999 to 2016, more than 630,000 people died from a drug overdose. Treatment for acute pain has been assessed in the ED, with review of several different pain medications. Sub-dissociative ketamine (SDK) has become a valuable treatment option for acute pain and in recent years, has been of increased interest due to the growing concerns regarding opioid abuse and opioid shortage in the United States. Sub-dissociative ketamine, an NMDA receptor antagonist, has been studied in dose ranges of 1-4.5 mg/kg for dissociative sedation, as well as dose ranges of 0.1-0.3 mg/kg to treat pain. The onset of action for an IV dose of 2 mg/kg has been studied, with onset usually within 30 seconds after injection and anesthetic effect lasting 5-10 minutes. Common side effects include elevated blood pressure, diplopia or nystagmus, nausea and vomiting. More rare and more severe side effects in dissociative doses include respiratory depression, emergency phenomenon, tonic and clonic movements, and anaphylaxis. However, these were rarely, if ever seen, findings in sub-dissociative doses. Several studies indicate that SDK is a safe and effective alternative to opioids for patients with complaints of moderate to severe pain that provides adequate analgesic effect by itself. In particular, several studies have compared SDK versus morphine, particularly looking at pain in individuals with abdominal pain, flank pain, low back pain or musculoskeletal pain, and acute fractures. SDK has also shown to decrease opioid consumption and the need for rescue analgesia. The studies showed that that there was no difference in average pain scores, but the amount of morphine required was significantly decreased. SDK has proven to be a safe alternative, but the side effects, although short, make it less desirable to use. To the investigator's knowledge, there has never been a study focusing on the use of combination fentanyl and SDK. Fentanyl, an opioid agonist, has been studied in low dose forms of 2 mcg/kg for pain, moderate dose forms of 2-20 mcg/kg for major surgical procedures, and high dose forms of 20-50 mcg/kg for orthopedic and open heart surgeries. Onset of action is almost immediate when given IV, and maximal effect of the drug may take several minutes. The usual duration of action is 30-60 minutes. Common side effects include hypertension, hypotension, dizziness, blurred vision, nausea, vomiting and laryngospasm. Serious side effects included respiratory depression, apnea, rigidity, bradycardia, serotonin syndrome, adrenal insufficiency, and if left untreated could cause cardiac arrest and circulatory depression. There have been several combination studies with SDK, but none regarding fentanyl and ketamine. In one study, combination SDK and reduced dose hydromorphone produced rapid pain relief without significant side effects. Another study indicated that morphine and SDK both provided adequate pain relief alone, but combined morphine and SDK required less morphine administration, had faster onset of relief, and provided sustained reduction in pain intensity for up to 2 hours.