Acetaminophen IV vs Hydromorphone IV in the ED

Inclusion Criteria: * Age 21 through 64 years of age: This is a study of adult ED patients. * Pain with onset within 7 days: Pain within seven days is the definition of acute pain that has been used in the ED literature. * ED attending physician's judgment that the patient's pain warrants IV opioids. * ED attending physician's judgment that the patient has capacity to provide informed consent. * Patients must be able to understand English or Spanish. Exclusion Criteria: * Use of opioids or tramadol within past 24 hours. * Use of acetaminophen or non-steroidal anti-inflammatory medication within the previous 8 hours. * Prior adverse reaction to opioids or acetaminophen. * Chronic pain syndrome: frequently recurrent or daily pain for at least 3 months results in modulation of pain perception which is thought to be due to down-regulation of pain receptors. Examples of chronic pain syndromes include sickle cell anemia, osteoarthritis, fibromyalgia, and peripheral neuropathies. * Medical condition that might affect metabolism or opioid analgesics or acetaminophen such as hepatitis, renal insufficiency or failure, hypo- or hyper-thyroidism, Addison's or Cushing's disease * Pregnant or breastfeeding * Alcohol intoxication: the presence of alcohol intoxication as judged by the treating physician may alter pain perception. * SBP \<100 mmHg: Opioids can produce peripheral vasodilation that may result in orthostatic hypotension. * HR \< 60/min: Opioids can cause bradycardia. * Oxygen saturation \< 95% on room air: For this study, oxygen saturation must be 95% or above on room air in order to be enrolled. * Use of MAO inhibitors in past 30 days: MAO inhibitors have been reported to intensify the effects of at least one opioid drug causing anxiety, confusion and significant respiratory depression or coma. * Patients using transdermal pain patches: pain patches may influence both the amount of pain patients report as well as the level of relief they obtain from other treatments. * Taking any medication that might interact with one of the study medications, such as SSRI or tricyclic anti-depressants, antipsychotics, anti-malarial medications (quinidine or halofantrine), amiodarone or dronedarone, diphenhydramine, celecoxib, ranitidine, cimetidine, ritanovir, terbinafine or St. John's Wort. * Patients who have been previously enrolled in this same study: Patients may only be enrolled once.