Drug metabolism involves the enzymatic conversion of therapeutically important chemical species to a new molecule inside the human body. The process may result in pharmacologically active, inactive, or toxic metabolite. Drug metabolic process involves two phases, the occurrence of which may vary from compound to compound. In this article, we discuss the basics of drug metabolism, the process, metabolising organs and enzymes (especially CYP450) involved, chemistry behind metabolic reactions, importance, and consequences with several interesting and significant examples to epitomize the same. We also cover the factors influencing the process of drug metabolism, structure-toxicity relationship, enzyme induction and inhibition.