APA Dictionary of Psychology

n. a chemical substance that is not naturally produced by the organism in which it is found. Xenobiotics can protect or restore health, as with antioxidants, medicines (e.g., antibiotics), or vaccines, or they can disrupt physical and mental systems, as in the case of pollutants in the water supply. The body often attempts to rid itself of xenobiotics via the process of xenobiotic metabolism, whereby the body’s enzymes break down the xenobiotic compound into more easily excreted products. In some cases, this process biologically activates the xenobiotic, which can result in health or harm, depending on the metabolic by-product. For example, sometimes breaking down the xenobiotic releases a toxic component of the compound into the body, causing illness. —xenobiotic adi.[from Greek xenos, stranger, and bios, life]