Analgesics can be classified as either opioid or non-opioid based on the mechanism of action. The non-opioid class of analgesics primarily consists of non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin and ibuprofen, and paracetamol, also known as acetaminophen. Both NSAIDs and paracetamol act as cyclooxygenase inhibitors and are notably different than opioid analgesics in that they have low abuse potential and are available without a prescription. Both naturally-occuring and synthetic opioid receptor ligands can act as opioid analgesics. Some of the more common opioid analgesics include morphine, codeine, oxycodone, fentanyl, and hydrocodone. The majority of medications in this class act as agonists of MOR, although many also have some activity at either DOR or KOR. The relative level of analgesia provided by each drug is determined by the specific half-life of the drug and the affinity for individual opioid receptors types. Due to the activation of MOR, these opioid medications are potentially addictive and, therefore, their use as analgesics is highly regulated.
