“I am now entering my fifth year as a regular heroin user,” writes Carl Hart in his revelatory new book, Drug Use for Grown-Ups. Fifty-four-year-old Hart is the Ziff professor of psychology at Columbia University. Regular heroin use and high academic achievement are not two pursuits that we expect to see in the same life story. At least not openly. Heroin is by popular consensus the worst of drugs, the one that leaves users hopelessly strung-out.