Non-steroidal anti-inflammatory drugs(NSAID) are members of a therapeutic drug class which reduces pain, decreases inflammation, decreases fever, and prevents blood clots. Side effects depend on the specific drug, its dose and duration of use, but largely include an increased risk of gastrointestinal ulcers and bleeds, heart attack, and kidney disease. The most prominent NSAIDs are aspirin, ibuprofen, diclofenac and naproxen, all available over the counter (OTC) in most countries. (Paracetamol (acetaminophen) is generally not considered an NSAID because it has only minor anti-inflammatory activity.)

The term non-steroidal, common from around 1960, distinguishes these drugs from corticosteroids, another class of anti-inflammatory drugs, which during the 1950s had acquired a bad reputation due to overuse and side-effect problems after their introduction in 1948.

NSAIDs work by inhibiting the activity of cyclooxygenase enzymes (the COX-1 and COX-2 isoenzymes). In cells, these enzymes are involved in the synthesis of key biological mediators, namely prostaglandins, which are involved in inflammation, and thromboxanes, which are involved in blood clotting.

There are two general types of NSAIDs available: non-selective and COX-2 selective. Most NSAIDs are non-selective, and inhibit the activity of both COX-1 and COX-2. These NSAIDs, while reducing inflammation, also inhibit platelet aggregation and increase the risk of gastrointestinal ulcers and bleeds. COX-2 selective inhibitors have fewer gastrointestinal side effects, but promote thrombosis, and some of these agents substantially increase the risk of heart attack. As a result, certain COX-2 selective inhibitors—such as rofecoxib—are no longer used due to the high risk of undiagnosed vascular disease. These differential effects are due to the different roles and tissue localisations of each COX isoenzyme. By inhibiting physiological COX activity, NSAIDs may cause deleterious effects on kidney function, and, perhaps as a result of water and sodium retention and decreases in renal blood flow, may lead to heart problems. In addition, NSAIDs can blunt the production of erythropoietin, resulting in anaemia, since haemoglobin needs this hormone to be produced.

NSAIDs are often suggested for the treatment of acute or chronic conditions where pain and inflammation are present. NSAIDs are generally used for the symptomatic relief of the following conditions:

The effectiveness of NSAIDs for treating non-cancer chronic pain and cancer-related pain in children and adolescents is not clear. There have not been sufficient numbers of high-quality randomised controlled trials conducted.

Differences in anti-inflammatory activity between the various individual NSAIDs are small, but there is considerable variation among individual patients in therapeutic response and tolerance to these drugs. About 60% of patients will respond to any NSAID; of the others, those who do not respond to one may well respond to another. Pain relief starts soon after taking the first dose, and a full analgesic effect should normally be obtained within a week, whereas an anti-inflammatory effect may not be achieved (or may not be clinically assessable) for up to three weeks. If appropriate responses are not obtained within these times, another NSAID should be tried.

Pain following surgery can be significant, and many people require strong pain medications such as opioids. There is some low-certainty evidence that starting NSAID painkiller medications in adults early, before surgery, may help reduce post-operative pain, and also reduce the dose or quantity of opioid medications required after surgery. Any increased risk of surgical bleeding, bleeding in the gastrointestinal system, myocardial infarctions, or injury to the kidneys has not been well studied. When used in combination with paracetamol, the analgesic effect on post-operative pain may be improved.