Opana ER 5mg capsules work 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. Opana Er 5mg is a powerful prescription painkiller that has been at the center of controversy in recent years. While it has been effective in managing chronic pain when used as prescribed, its addictive properties and high potential for abuse have led to widespread misuse and devastating consequences.