Chronic use of NSAIDs including low-dose aspirin is associated with gastrointestinal mucosal injury. However, major adverse events are relatively infrequent. Patients with multiple risk factors such as a previous history of peptic ulcer disease, increasing age, co-prescription of corticosteroids and anticoagulants, and high-dose and long-term use of NSAIDs are at the highest risk of major gastrointestinal toxicity. In patients with multiple risk factors, physicians need to assess these risks before prescribing NSAIDs and adopt risk-minimising strategies.
NSAIDs have anti-inflammatory (reduce inflammation), analgesic (relieve pain) and antipyretic (lower temperature) effects. Although different NSAIDs have different structures, they all work by blocking cyclooxygenase (COX) enzymes. There are two main types of COX enzymes: COX-1 and COX-2. Both types produce prostaglandins; however, the main function of COX-1 enzymes is to produce baseline levels of prostaglandins that activate platelets and protect the lining of the gastrointestinal tract, whereas COX-2 enzymes are responsible for releasing prostaglandins after infection or injury. Prostaglandins have a number of different effects, one of which is to regulate inflammation. Most NSAIDs inhibit both enzymes, although a few are available that mainly inhibit COX-2. The pain-relieving and anti-inflammatory effects of NSAIDs are mainly due to inhibition of COX-2, and their unwanted side effects are largely due to inhibition of COX-1.
NSAIDS have antipyretic activity and can be used to treat fever.   Fever is caused by elevated levels of prostaglandin E2 , which alters the firing rate of neurons within the hypothalamus that control thermoregulation.   Antipyretics work by inhibiting the enzyme COX, which causes the general inhibition of prostanoid biosynthesis ( PGE2 ) within the hypothalamus .   PGE2 signals to the hypothalamus to increase the body's thermal set point.   Ibuprofen has been shown more effective as an antipyretic than paracetamol (acetaminophen).   Arachidonic acid is the precursor substrate for cyclooxygenase leading to the production of prostaglandins F, D & E.