Hydrocodone is a prescription opioid used to treat certain types of pain. Because it can cause drowsiness, respiratory depression, physical dependence, misuse, and overdose, it should only be used under appropriate medical supervision. Hydrocodone is a prescription opioid used to treat certain types of pain. Because it can cause drowsiness, respiratory depression, physical dependence, misuse, and overdose, it should only be used under appropriate medical supervision.