Once upon a time there was a boy and a girl and they were in love and neither had ever taken drugs. When the boy turned 21 he celebrated by having his first ever ecstasy pill. He had a good time, but his girlfriend didn’t really understand why he couldn’t get his act together a couple of days later when he was coming down. Fast forward a few months and the boy suggested to the girl that she could try a pill too, to see what this business was all about. She too liked it, and now understood why coming down felt like wading through muddy sludge.

The boy and girl continued to be in love and started partying together. They had strict rules – they couldn’t take drugs more often than once a month, and they had limits on how much drugs they would have at one time. They took ecstasy and speed, had long happy nights out dancing, and lots of cuddles and comfort food through the come downs. Eventually, they broke up.

The boy kept taking drugs, he experimented with different types of drugs in different combinations, he even injected meth a few times. But he never broke his once-a-month rule and never got into any financial, legal, medical or relationship difficulties because of his use. His (ex) girlfriend kept taking drugs too. She developed a liking for injecting meth. In fact, she got addicted. She would go on weekly binges – not sleeping or eating for days, before crashing into exhaustion and depression. She held down a good job, but was frequently broke, couldn’t maintain a relationship and did damage (some of it permanent) to her health.

The boy and the girl were not so very different when they first started taking drugs, but they ended up in very different places. Why is it that some people get addicted to drugs, and others never do? Is it the sort of thing you can predict – about another person, about yourself – before you even start? And is there something more, or different, that governments and health services should be doing to help people avoid getting addicted in the first place? Is there ever any way to prevent addiction?