Opana ER 5 mg is a prescription medication containing oxymorphone, a powerful opioid analgesic used for managing severe pain in patients who require around-the-clock pain relief. It is designed for extended release, for long-lasting pain relief. However, due to its high potential for abuse, addiction, and overdose, Opena er 5 mg pills should be used only as directed by a healthcare provider. Common side effects include nausea, dizziness, constipation, and respiratory depression, particularly when misused or taken with other sedatives.