How paracetamol works

As with many medicines, the effectiveness of paracetamol was discovered without knowing how it works. Its precise mode of action is still unclear, although, like aspirin, it is thought to inhibit the enzyme cyclo-oxygenase and thus reduce prostaglandin synthesis, the hormone-like mediators of pain, fever and inflammation. Paracetamol effectively produces analgesia by elevating the pain threshold and reduces fever by 'resetting' the hypothalamic heat-regulating centre of the brain.

Although aspirin and paracetamol are thought to exert their effects through inhibition of prostaglandin synthesis, there are some differences. Whereas aspirin acts both centrally and peripherally, paracetamol probably acts mainly in the central nervous symptom. In addition, whereas paracetamol and aspirin have comparable analgesic and antipyretic properties, increasing the dose of paracetamol does not produce anti-inflammatory effects, probably due to its lack of peripheral activity.

Whereas aspirin and other NSAIDs can exacerbate gastric damage and should not be used in patients with an ulcer, paracetamol does not pose a problem in these patients, again presumably because it lacks significant peripheral activity.