Xenobiotics are artificial substances that are foreign to an entire biological system, that is, not produced by or within the body itself. For example, antibiotics in case of a human body.Antibiotics are resistant to microbial attack. So they are administered as drugs.
Also, substances if present in higher concentrations than usual can also be grouped into xenobiotics.
Xenobiotics find many uses in our daily lives as food additives, drugs and pesticides.