Xenobiotic metabolism is the set of metabolic pathways that modify the chemical structure of xenobiotics, which are compounds foreign to an organism's normal biochemistry, such as any drug or poison. These are a form of biotransformation present in all major groups of organisms and are considered to be of ancient origin. These reactions often act to detoxify poisonous compounds although in some cases the intermediates in xenobiotic metabolism can themselves cause toxic effects.. Most of these chemicals that gain access to the body via the diet, air, drinking water, drug administration, and lifestyle choices, undergo a broad range of processes of detoxication that in general render them less toxic, more polar, and readily excretable.