How do opiates block sensations of pain?

Mechanism of action: Although the primary effects of opioids are in the CNS (mu, kappa, and delta receptors), and opioid receptors are also upregulated and transported to the peripheral terminals of C-fibers and A-delta fiber especially during the process of inflammation. By activating opioid receptors in the periphery, administration of opioids can result in significant analgesia.