Vicodin is a prescription opioid pain medication that is commonly used to treat moderate to severe pain. It is a combination of two medications: hydrocodone and acetaminophen. Hydrocodone is an opioid that binds to opioid receptors in the brain and spinal cord, blocking pain signals. Acetaminophen is a non-opioid pain reliever that works by inhibiting the production of prostaglandins, chemicals that cause pain and inflammation.