"Addiction is not a disease"

Lewis, 65, is now based at Radboud University in the Netherlands. Softly spoken and grey-bearded, he has a calm aura, which is probably the result of the meditation he regularly practises, and which he used to help himself overcome his addiction at 30.

I got arrested the third time I smoked dope

It is hard to imagine him as a self-confessed "bad kid", who wore his injection bruises "like a badge of courage".

Lewis's family were strongly, culturally Jewish. He went to Hebrew classes and even to a Jewish day school but, after his barmitzvah, he recalls, he'd "had enough" of religion. At 15, he was enrolled in a US boarding school, and it was there that the "intersection point" between his Judaism and his history of addiction occurred. "It was a horrible experience," he says.

"There was a lot of bullying and antisemitism. I was knocked over by it and really became quite depressed, and that was how I would frame the beginning of my years of addiction."

He first experimented with alcohol and cough medicine, before trying marijuana. "I actually got arrested the third time I ever smoked dope. Naively, I didn't know that it had an odour. I was sitting on the toilet in a restaurant in downtown New York, and suddenly the police were pounding on the door. I was dragged off to jail and my dad had to come and bail me out."

That traumatic experience didn't put him off. "It rarely does," he claims. "Using punishment and consequence to try to stem addiction is universally unsuccessful. It actually sweetened the pot because now I could see myself as a bad kid."

By the time he got to The University of California, Berkeley, it was 1968 and "drugs were flowing down the streets". For Lewis, the lure was irresistible. "I was a mixed-up kid, depressed, anxious, not sure how to socialise. Berkeley was a Mecca - I thought: 'This is for me, now I know where I'm going.'"

Enchanted by LSD, it wasn't long before he graduated to more serious drugs. "One day, a guy asked me if I wanted to try heroin. I said OK, knowing people would disapprove - but for me that was another thrill. I didn't imagine I would get addicted, that old story. Drugs were just a big adventure. The first time, I wondered what all the fuss was about but, by the third, it started to become attractive to me: the whole ritual of preparing it, injecting and so forth."

Psychological addiction crept up on him. "It was a strange double life. I was still functioning, working, getting good grades at college. But at night I was taking heroin, other opiates, and/or cocaine." He'd make promises to stop, then lapse. "I was rationalising, trying to find loopholes in my commitments to quit. I was still self-aware enough to recognise that this was not good."

He spiralled further into addiction, wrecking his academic career when, as a graduate psychology student living in the psychiatric hospital where he worked, he got caught stealing drugs from a medical centre. In order to keep out of jail, he had to get character references from his professors. But, of course, then everybody knew he was an addict, and so he got thrown out of university.

He went home to Toronto, worked as a window cleaner and house painter and, for several years, continued his cycle of addiction and abstinence. And then, soon after he had started working in homes for troubled kids, he had an epiphany: he'd had enough of his addiction. He calls it an emotional reorientation. "I just got to the point that I was sick of it, disgusted with it. My first marriage had failed, my girlfriend had left me. I was angry and determined not to do it any more. And so I stopped."

He quit, on his own, helped by practising Tai Chi and meditation and by marking off his drug-free days on a calendar, until he became confident that he had broken the habit. He reapplied to grad school and, to his surprise, was accepted. After gaining a PhD in child clinical psychology, he went on to become a professor of developmental psychology, specialising in children, then switching to neuroscience.

It was partly his research in child development that led him to formulate his ideas about addiction. "I became aware that the brain changes all the time with emotional experiences, learning, and significant events in people's lives.

"When I looked at addiction from this point of view, I could see that the brain is not diseased, it is simply learning new habits and forming new pathways. While some drugs can be physically addictive, chemical dependency is only a small part of it. People can be addicted to gambling, porn, shopping, and drugs that do not produce withdrawal symptoms."

What is addiction, if not a disease?

"It's not 'a something'. If someone asked:'What is sex?' you'd have a hard time giving it a category; it's its own thing. Addiction is like that, too, it's a part of life, it's a tendency to develop very strong habits of attraction for a substance or an activity that is fulfilling, rewarding or brings relief. It's a habit of mind, of thought, an attitude.

"Fundamentally, it's a belief: I believe that if I do x I will feel better, and nothing else will make me feel better. It's learned behaviour. There are brain changes, of course. The whole neuro-chemical reward system becomes tuned to these specific rewards, whether it's drugs, booze, or sex."

He is adamant that there is no such thing as an "addictive personality".

"Yes, there is a genetic component - as there is to everything - and some people are more likely to become addicts than others, those who are more impulsive, for example; but there is no addictive gene. People who have a perfectly lovely life don't usually become addicts. It's usually those with psychological difficulties, those who have suffered trauma, or abuse, or neglect - people who have not learned how to make themselves feel OK."

His is a controversial view. The accepted "chronic brain disease" model of addiction fuels the billions that are spent each year, worldwide, on scientific research and treatment programmes; a huge industry. Lewis says that it doesn't work.

"If you call addiction a disease, you're saying: 'It's not your fault, you can't help being sick.' There's a fatalism in disease; you've got it for life, so being an addict becomes your defining characteristic. It's disadvantageous to people who need to gather their commitment and effort and self-control to fight it.

"Doctors do have a role to play but doctors don't have the tools to fight the main problem: psychological addiction. There's no pill to stop people wanting something."

While some addicts do need help to quit, he says, many - like himself - do so without any formal treatment at all.

"We need to support people psychologically and practically, teach them to live with themselves, help them to connect. Ultimately, quitting is about finding will-power, winning the tug of war between compulsion and the desire to stop."

Today, Lewis regards himself as "Jewish by background". He's brought his children up to meditate, rather than go to synagogue.

"We still do Seder, when we're back in Toronto, and we have Rosh Hashanah dinner with family."

His wife, Isabela Granic, is a professor of developmental psychology, and they have twin boys of 10. He also has a 28-year-old daughter who lives in Toronto.

"I don't discuss drugs with the boys," he says. "My daughter recognises my period of addiction as a difficult time in my past, something I had to work through.

"I hope that helps give her direction and wisdom when she, like most other young adults, works out her own attitude toward recreational drugs."

Was Karl Marx right when he described religion as the opiate of the masses? Is being religious a form of addiction?

"Yes, in the way that religion can become a focus, a habit, a way to alleviate personal turmoil. Believing in a god that is there for you must be tremendously reassuring, so it can work like a drug.

"But I don't think religion is a bad thing. Sometimes people just need to feel more secure."

'The Biology of Desire, Why Addiction Is Not a Disease' by Marc Lewis (Scribe UK £9.99)