An analgesic or painkiller is any member of the group of drugs used to achieve analgesia, relief from pain.
Analgesic drugs act in various ways on the peripheral and central nervous systems. They are distinct from anesthetics, which reversibly eliminate sensation. Analgesics include paracetamol (known in the US as acetaminophen or simply APAP), the non-steroidal anti-inflammatory drugs (NSAIDs) such as the salicylates, and opioid drugs such as morphine and oxycodone.
Morphine, the archetypal opioid, and various other substances all exert a similar influence on the cerebral opioid receptor system. Buprenorphine is thought to be a partial agonist of the opioid receptor, and tramadol is an opiate agonist with SNRI properties. Tramadol is structurally closer to venlafaxine than to codeine and delivers analgesia by not only delivering “opiate-like” effects but also by acting as a weak but fast-acting serotonin releasing agent and norepinephrine reuptake inhibitor. Tapentadol, with some structural similarities to tramadol, presents what is believed to be a novel drug working through two (and possibly three) different modes of action in the fashion of both a traditional opioid and as a SNRI. The effects of serotonin and norepinephrine on pain, while not completely understood, have had causal links established and drugs in the SNRI class are commonly used in conjunction with opioids (especially tapentadol and tramadol) with greater success in pain relief. Dosing of all opioids may be limited by opioid toxicity (confusion, respiratory depression, myoclonic jerks and pinpoint pupils), seizures (tramadol), but opioid-tolerant individuals usually have higher dose ceilings than patients without tolerance.
