Opioid drugs act on the opioid receptors present in the central and peripheral nervous system. The drug class primarily used in relieving pain includes natural, semi-synthetic, and synthetic opioids. Codeine, morphine, hydrocodone, oxycodone, heroin, and fentanyl are some of the major prescription drugs in the global opioids agonist drugs market. Opioids can be administered as oral pills, parenteral, liquids, patches, or lozenges.
