“We could explain why the crime rate dropped,” said Marks.  “We could explain why there were fewer deaths—they were getting clean heroin instead of rubbish.  But what we couldn't understand was the reduction in the incidence of new cases. It seemed to prevent the spread of addiction.  And we just thought we'd done the experiment wrong.  But when we consulted official statistics—both American and English and other foreign statistics—we found identical results: that if you loosened up a little bit on drug issues, you actually got a fall in the incidence of addiction.  But if you loosened up too much, and made it freely available like we now have with alcohol, it started to rise again.”^[13]

What Marks realized was that the demand curve for forbidden fruit is not linear—it's U-shaped.  If drugs and alcohol are too freely available—or if they’re prohibited—you increase consumption. “Free markets promote use; prohibitions pedal use.  And I discovered quite by accident the validity of this at the Widnes clinic.”

One a typical Tuesday morning in March, seven drug addicts wind their way up the narrow stairs to the second floor clinic on Chapel Street. They’re here to pick up their weekly prescriptions, but first they’ll have to sit in on a group session—not therapy exactly—just a little chat so the staff can eyeball them and see how they’re doing. As they pull their chairs into a circle in the cluttered conference room, they are indistinguishable from any other seven citizens on the streets of Liverpool. Nothing in their appearance or behavior would suggest that they are serious addicts. Among them is a round-faced Irish brunette with a wry smile named Julie. Well-dressed, in her mid-thirties, she could easily be taken for a businesswoman or a teacher, but something about her eyes suggests broader experience.  Julie shoots heroin once a day.