Paracetamol is generally considered to be a weak inhibitor of the enzyme cyclooxygenase-2 (COX-2). This enzyme is important in the synthesis of prostaglandins (PG), so by inhibiting the action of COX-2, paracetamol causes a decrease in PG production. Prostaglandins are important mediators of inflammation, and their release has many effects including the sensitisation of nerve cells to pain, and a direct effect on the hypothalamus in the brain resulting in fever.
What is the effect of paracetamol on the human body? – http://wiki.answers.com/Q/What_is_the_effect_of_paracetamol_on_the_human_body