The purpose of the current study is to compare the analgesic efficacy of intravenous acetaminophen and intravenous hydromorphone in the treatment of acute pain in the ED.

This is a randomized, double-blind placebo-controlled clinical trial comparing intravenous acetaminophen and intravenous hydromorphone in the treatment of acute pain in the Emergency Department. Enrolled subjects presenting to the ED with acute pain will be randomized to receive either acetaminophen 1g IV or hydromorphone 1mg IV.

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.