When I was young, I drank to get wrecked. In the hospitals in the 1980s and 1990s, I witnessed the complications of heroin addiction: amputations, gangrene, endocarditis, sepsis, hepatitis, and HIV. A stream of ambulances spilt half dead overdosers onto accident and emergency trolleys. There was no drug for opioid substitution—for example, methadone—so addicts had to “take the rattle.” Many patients took irregular discharge while acutely unwell. But they were just junkies, and the sheer scale of the problems blunted me to the suffering and the deaths. It was the same when working …