There's a perfectly adequate answer. It relies on a lot of genetics, a lot of maths and statistics and a large dose of simple common sense, all of which sum to the fact that we are all inescapably, at the levels of both nature (genetic makeup) and nurture (life experiences), thoroughly accidental and contingent beings who by sheer chance could have been otherwise or never have been at all.
A narcotic is anything that eases discomfort, numbs the critical faculties, deadens the perception of reality and in large doses induces stupor.