Opana ER 30 mg is a prescription medication used to treat moderate to moderately severe pain. It is classified as an opioid analgesic, but it also has some unique properties that differentiate it from other opioids. Opana ER 30 mg capsules works by binding to opioid receptors in the brain and spinal cord, but it also inhibits the reuptake of serotonin and norepinephrine, which are neurotransmitters involved in the modulation of pain signals.