An<unk>  is a molecule capable of slowing or preventing the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons from a substance to an oxidizing agent. Oxidation reactions can produce free radicals, which start chain reactions that damage cells.<unk> s terminate these chain reactions by removing free radical intermediates, and inhibit other oxidation reactions by being oxidized themselves. As a result,<unk> s are often reducing agents such as thiols or polyphenols.
Although oxidation reactions are crucial for life, they can also be damaging; hence, plants and animals maintain complex systems of multiple types of<unk> s, such as glutathione, vitamin C, and vitamin E as well as enzymes such as catalase, superoxide dismutase and various peroxidases. Low levels of<unk> s, or inhibition of the<unk>  enzymes, causes oxidative stress and may damage or kill cells.
As oxidative stress might be an important part of many human diseases, the use of<unk> s in pharmacology is intensively studied, particularly as treatments for stroke and neurodegenerative diseases. However, it is unknown whether oxidative stress is the cause or the consequence of disease.<unk> s are also widely used as ingredients in dietary supplements in the hope of maintaining health and preventing diseases such as cancer and coronary heart disease. Although some studies have suggested<unk>  supplements have health benefits, other large clinical trials did not detect any benefit for the formulations tested, and excess supplementation may be harmful. In addition to these uses in medicine,<unk> s have many industrial uses, such as preservatives in food and cosmetics and preventing the degradation of rubber and gasoline.
Antioxidant
Antimetabolite
Radionuclide
Substrate 
Phytochemical
Immunostimulator
Stimulant
Immunoconjugate