Cells generate energy by reducing molecular oxygen to water. During the process, small amounts of partially reduced reactive oxygen forms are produced as unavoidable byproducts which are referred to as Reactive Oxygen Species. An imbalance between free radical-generating and radical scavenging systems results in Oxidative Stress. Reactive nitrogen species and other non reactive derivatives are also involved. These processes lead to tissue damage and contribute to the pathogenesis of many disorders like hypertension, cancer, diabetes, neurodegenerative disorders and others. The human body has several mechanisms to counter the effects of these reactive species by the production of antioxidant enzymes like glutathione and catalase. Antioxidants can also be taken exogenously through the diet. This article provides an overview of the different free radicals known, the mechanism by which they cause tissue damage and the protective role played by different antioxidants.

The aqueous extract of Swertia chirata Buch Ham. Root (ASC) (Family: Gentianaceae) was evaluated for its antipyretic potential on Brewer's yeastinduced pyrexia in albino rats and Typhoid-Paratyphoid A, B vaccine induced Hyperexia in rabbits. In both models, the extract, at dose of 200 mg kg −1 body wt. and 400 mg kg −1 body weight, produced significant (p<0.001) reduction in elevated body temperature in a dose dependent manner. The antipyretic effect of the extract was comparable to that of paracetamol (150 mg kg −1 body weight, p.o.), a standard antipyretic agent.