Here’s one example of an experiment that is happening all around you, and may well happen to you one day. If you get run over today and you break your hip, you will probably be given diamorphine, the medical name for heroin. In the hospital around you, there will be plenty of people also given heroin for long periods, for pain relief. The heroin you will get from the doctor will have a much higher purity and potency than the heroin being used by street-addicts, who have to buy from criminals who adulterate it. So if the old theory of addiction is right — it’s the drugs that cause it; they make your body need them — then it’s obvious what should happen. Loads of people should leave the hospital and try to score smack on the streets to meet their habit.