Opana ER (extended-release) is the brand name for the prescription medication oxymorphone hydrochloride. It is an opioid analgesic used for the management of moderate to severe pain when continuous, around-the-clock pain relief is needed for an extended period. Opana ER is an extended-release formulation, which means it releases the medication slowly over an extended period, providing longer-lasting pain relief compared to immediate-release opioids.