How do opioids work and what are their major risks?

Opioids relieve pain by binding to mu, kappa, and delta opioid receptors in the brain, spinal cord, and peripheral tissues, reducing the perception of pain and the emotional response to it. Common opioids include morphine, oxycodone, hydrocodone, fentanyl, and codeine. Major risks include respiratory depression, which is the primary cause of opioid overdose death; physical dependence developing within days to weeks of regular use; constipation that persists throughout treatment without tolerance developing; and sedation. Naloxone is the reversal agent.