3 ideas
Lee insists nobody becomes addicted from a single good experience; you become a junky because you have no strong motivation in any other direction, and dependence builds through months of casual repeated use. The habit is a way of life that fills a vacuum of purpose, and the pleasure of the drug matters less than the relief of the need it creates.
By recording sickness, scoring, informers, and cures in affectless, reportorial prose with no confession or redemption arc, the narrative denies the reader the comfort of a moral lesson. Removing judgment makes the subculture's internal logic (jargon, rituals, the traffic between users, pushers, and police) visible as a working system rather than a cautionary tale.
In 1940s New York, Lee is handed stolen morphine syrettes to sell, tries them, and gradually becomes addicted, then works the subway rolling drunks and pushing heroin to support the habit. Arrests and prescription-forging charges drive him to Texas and New Orleans, repeated withdrawals and cures fail, and he ends up in Mexico City, where a tightening legal climate leaves him heading for South America in search of yage, a drug he hopes will offer the kind of insight junk never did.