Casual, as in a one to two times a week for a few months. The researchers at Harvard Medical School found that parts of the brain responsible for emotion, motivation and addiction were negatively affected when cannabis was introduced.
Researchers carried out detailed 3D scans on the brains of students who used cannabis casually and were not addicted and compared them with those who had never used it.
Two major sections of the brain were found to be affected.
The scientists found that the more cannabis the 40 subjects had used, the greater the abnormalities.
Around 10 million people in Britain, almost a third of the population, have used illegal drugs, with cannabis the most popular. The research author, Dr Hans Breiter, professor of psychiatry and behavioural sciences at Northwestern University Feinberg School of Medicine, 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 OK 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.
