“I started smoking at 14 for the same reason as most people do. All my friends were into it. From the age of 17 till about 20, I was smoking an eighth (of an ounce) a day, including lunchtimes, to make school bearable.

It became a lot harder to deal with being stoned when I was doing my A-levels. I’d read the same page 14 times because I just couldn’t concentrate. One time, I fell asleep on my desk and the teacher held me back after class and said, ‘I don’t know what you’re doing, but whatever it is, it’s messing you up.’ I felt stupid.

“I’d sit there obsessing about something, getting paranoid and anxious and then suddenly I’d see a spider on the wall and I’d forget what I’d been thinking about. About a year and a half ago, I had an anxiety attack. I didn’t sleep for two weeks and had to go on Valium. It was then that I stopped smoking and haven’t smoked since, except for the occasional puff, but I don’t enjoy it any more. It takes me straight back into a state where I’m losing the plot. I want to get on with my life now. I need to use my brain, and weed stops that from happening.”

Babatunde is 27 and studying alternative medicine in east London. He is a paranoid schizophrenic who is on daily medication.

“I was born in London but was sent to be educated in Nigeria between the ages of nine and 18. My brother, a medical student, introduced me to cannabis when I was 23, and from then I got into smoking a lot of skunk.

I’d see auras around my body and soon was getting hallucinations and delusions. I thought the television was talking to me. But I didn’t make the connection between the weed and these strange things.

“My mum got worried about me and after a GP visit I was referred for psychiatric observation. I was sectioned at the local hospital, which meant 28 days on the ward. I ran away, but the police took me back.

“Since then, I’ve been sectioned another four times and have been on medication, but until five or six months ago I carried on smoking, including on the psychiatric wards. In Nigeria, people associate smoking with going mad. I didn’t believe it then. But I do now.”

Hannah is the mother of Sean, a 19-year-old from Oxford who has been smoking cannabis for years.

“I have known there was something wrong since Sean was 14. From being a bright and motivated lad, he became moody and got bad school reports. I knew that he’d been smoking skunk and had tried to get him to stop, but he wouldn’t.

“It reached rock bottom when he had a breakdown a few months ago. First he became paranoid and aggressive and then he cut himself, not badly but enough to frighten him. From that moment, he stopped smoking skunk. Since then he’s been on an even keel, but still puffs weaker spliffs occasionally. He says he has things under control, but seeing him so out of control has left me feeling that I’m living alongside an active volcano.”