Lowdown on the dagga high

17 April 2014 - 09:45 By Rebecca Smith
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Experimenting with cannabis on a casual basis damages the brain permanently, research has found.

Medical experts said even people who had only used cannabis once or twice a week for a few months experienced changes in the parts of the brain that govern emotion, motivation and addiction.

Researchers from Harvard Medical School in the US carried out detailed 3D scans on the brains of 40 students who used cannabis casually and were not addicted, and compared those results with the brain scans of people who have never used cannabis.

Two major sections of the brain were found to be affected.

The greater the use, the greater the abnormalities the scientists found.

Around 10 million people in Britain, almost a third of the population, have used illegal drugs, with cannabis being the most popular.

Dr Hans Breiter, a professor of psychiatry and behavioural sciences at the Northwestern University Feinberg School of Medicine in Chicago, said: "This study raises a strong challenge to the idea that casual marijuana use isn't associated with bad consequences. Some people only used marijuana to get high once or twice a week.

"People think a little recreational use shouldn't cause a problem, if someone is doing okay with work or school. Our data directly says this is not the case. I've developed a severe worry about whether we should be allowing anybody under age 30 to use pot unless they have a terminal illness and need it for pain."

The team examined sections of the brain involved in emotion, motivation and addiction in 20 students who had used cannabis and 20 who had not.

Anne Blood, assistant professor of psychiatry at Harvard Medical School, said: "These are core, fundamental structures of the brain. They form the basis for how you assess positive and negative features about things in the environment and make decisions about them."

The changes are thought to be the first steps towards addiction as the brain alters the way it perceives reward and pleasure, making ordinary experiences seem less fulfilling compared with drug use.

Jodi Gilman, a researcher in the Massachusetts General Centre for Addiction Medicine, said: "It may be that we're seeing a type of drug learning in the brain. We think when people are in the process of becoming addicted, their brains form these new connections.

"Drug abuse can cause more dopamine release than natural rewards like food, sex and social interaction. That is why drugs take on so much salience, and everything else loses its importance."

The study is published in the Journal of Neurosciences.

Mark Winstanley, chief executive of Rethink Mental Illness, said: "Research also shows that when people smoke cannabis before the age of 15, it quadruples their chance of developing psychosis. But very few people are aware of the risks involved."

Professor David Nutt, from Imperial College, London, said a sample of 40 was not big enough to draw conclusions.

Nutt, who was sacked as a government drugs adviser for his views, said: "Whatever cannabis does to the brain, it's not in the same league as alcohol, which is a proven neurotoxin."  The Daily Telegraph

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