John Marks is an English doctor who treated drug addicts by prescribing them heroin for many years, until the U.S. persuaded the U.K. government to shut down his program. Still, Marks saw how the program transformed his patients’ lives. It gave them a safe and reliable heroin supply, eliminated their need to commit crimes or do sex work to pay for the drug, and freed up their time for other pursuits like work and education. In short, he learned that heroin addicts can live ordinary, stable lives if they receive heroin through a prescription rather than through the black market. His work is an important model for drug legalization efforts, and it inspired Ruth Dreifuss’s decision to create a nationwide system of heroin clinics in Switzerland.