analgesic analgesic an analgesic drug, also called simply an analgesic (american english), analgaesic (british english), pain reliever, or painkiller, is any member of the group of drugs used to achieve relief from pain (that is, analgesia or pain management). analgesics are conceptually distinct from anesthetics, which temporarily reduce, and in some instances eliminate, sensation, although analgesia and anesthesia are neurophysiologically overlapping and thus various drugs have both analgesic and anesthetic effects. for the medical condition of hereditary analgesia, see congenital insensitivity to pain. analgesicdrug classopium poppies such as this one provide ingredients for the class of analgesics called opiatesclass identifiersusepainatc coden02aclinical datadrugs.comdrug classesconsumer reportsbest buy drugswebmdmedicinenet in wikidata analgesic choice is also determined by the type of pain: for neuropathic pain, traditional analgesics are less effective, and there is often benefit from classes of drugs that are not normally considered analgesics, such as tricyclic antidepressants and anticonvulsants. various analgesics, such as many nsaids, are available over the counter in most countries, whereas various others are prescription drugs owing to the substantial risks and high chances of overdose, misuse, and addiction in the absence of medical supervision. etymology the word analgesic derives from greek an- (ἀν-, "without"), álgos (ἄλγος, "pain"), and -ikos (-ικος, forming adjectives). such drugs were usually known as anodynes before the 20th century. classification analgesics are typically classified based on their mechanism of action.a bottle of acetaminophen. paracetamol (acetaminophen) main article: paracetamol paracetamol, also known as acetaminophen or apap, is a medication used to treat pain and fever. it is typically used for mild to moderate pain. in combination with opioid pain medication, paracetamol is now used for more severe pain such as cancer pain and after surgery. it is typically used either by mouth or rectally but is also available intravenously. effects last between two and four hours. paracetamol is classified as a mild analgesic. paracetamol is generally safe at recommended doses. nsaids main article: nonsteroidal anti-inflammatory drug nonsteroidal anti-inflammatory drugs (usually abbreviated to nsaids), are a drug class that groups together drugs that decrease pain and lower fever, and, in higher doses, decrease inflammation. the most prominent members of this group of drugs, aspirin, ibuprofen and naproxen, are all available over the counter in most countries. cox-2 inhibitors main article: cox-2 inhibitor these drugs have been derived from nsaids. the cyclooxygenase enzyme inhibited by nsaids was discovered to have at least two different versions: cox1 and cox2. research suggested most of the adverse effects of nsaids to be mediated by blocking the cox1 (constitutive) enzyme, with the analgesic effects being mediated by the cox2 (inducible) enzyme. thus, the cox2 inhibitors were developed to inhibit only the cox2 enzyme (traditional nsaids block both versions in general). these drugs (such as rofecoxib, celecoxib, and etoricoxib) are equally effective analgesics when compared with nsaids, but cause less gastrointestinal hemorrhage in particular. after widespread adoption of the cox-2 inhibitors, it was discovered that most of the drugs in this class increase the risk of cardiovascular events by 40% on average. this led to the withdrawal of rofecoxib and valdecoxib, and warnings on others. etoricoxib seems relatively safe, with the risk of thrombotic events similar to that of non-coxib nsaid diclofenac. opioids main article: opioid morphine, the archetypal opioid, and other opioids (e.g., codeine, oxycodone, hydrocodone, dihydromorphine, pethidine) all exert a similar influence on the cerebral opioid receptor system. buprenorphine is a partial agonist of the μ-opioid receptor, and tramadol is a serotonin norepinephrine reuptake inhibitor (snri) with weak μ-opioid receptor agonist properties. tramadol is structurally closer to venlafaxine than to codeine and delivers analgesia by not only delivering "opioid-like" effects (through mild agonism of the mu receptor) 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 an 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. opioids, while very effective analgesics, may have some unpleasant side-effects. patients starting morphine may experience nausea and vomiting (generally relieved by a short course of antiemetics such as phenergan). pruritus (itching) may require switching to a different opioid. constipation occurs in almost all patients on opioids, and laxatives (lactulose, macrogol-containing or co-danthramer) are typically co-prescribed. when used appropriately, opioids and other central analgesics are safe and effective; however, risks such as addiction and the body's becoming used to the drug (tolerance) can occur. the effect of tolerance means that frequent use of the drug may result in its diminished effect. when safe to do so, the dosage may need to be increased to maintain effectiveness against tolerance, which may be of particular concern regarding patients with chronic pain and requiring an analgesic over long periods. opioid tolerance is often addressed with opioid rotation therapy in which a patient is routinely switched between two or more non-cross-tolerant opioid medications in order to prevent exceeding safe dosages in the attempt to achieve an adequate analgesic effect. opioid tolerance should not be confused with opioid-induced hyperalgesia. the symptoms of these two conditions can appear very similar but the mechanism of action is different. opioid-induced hyperalgesia is when exposure to opioids increases the sensation of pain (hyperalgesia) and can even make non-painful stimuli painful (allodynia). alcohol