ANALGESICS are drugs that relieve the sensation of pain. Because pain is a subjective experience, arising from many causes, there are many ways that drugs can be used to relieve it. However, the term analgesic is best restricted, from a pharmacological point of view, to two main classes of drugs.

(1) Narcotic analgesics or opioid analgesics, typified by morphine, have powerful actions on the CNS, and act to alter the perception of pain. Because of the numerous possible side-effects, crucially dependence (habituation, ‘addiction’), this class is usually used under strict medical supervision and are only available on prescription or OTC in very low doses.

(2) Non-narcotic analgesics (NSAIDs), typified by aspirin, which have no tendency to produce dependence, but are by no means free of side-effects. This class is referred to by many names, most commonly non-steroidal antiinflammatory drugs (NSAIDs). The latter term refers to the valuable antiinflammatory action of some members of the class. This class is used for a variety of purposes, such as treating mild aches and pains, for fever (see ANTIPYRETICS) and rheumatoid arthritis (at higher dosages), see ANTIINFLAMMATORY AGENTS. Apart from these two main classes, there are other drugs that are sometimes referred to as analgesic because of their ability to relieve pain (e.g. local anaesthetics are sometimes referred to as local analgesics in the USA). Also, COUNTER-IRRITANTS (rubefacients) may be called analgesics, though their exact mechanism of action is not clear. Some specific sorts of pain respond to unusual agents not normally classified as analgesics; e.g. carbamazepine in the treatment of trigeminal neuralgia. Many other mechanisms of analgesic action are theoretically, or experimentally, possible. See also NSAID ANALGESIC; OPIOID ANALGESIC.