Long term dope use shrinks the brain

Jun 3 2008

According to Australian researchers the long term use of marijuana may cause parts of the brain which control memory, emotion and aggression, to shrink.

The researchers from the Universities of Melbourne and Wollongong have found that people who smoke more than five joints a day for at least 10 years, had a smaller hippocampus and amygdala which are responsible for emotion and memory and regulating fear and aggression.

The scientists used magnetic resonance imaging (MRI) to scan the brains of 15 marijuana smokers with an average age of 40 and 16 individuals who did not use the drug.

The marijuana users had smoked in excess of five joints a day for at least 10 years and had on average a 12% smaller hippocampus, and a 7% smaller amygdala - they had used other illicit drugs less than 10 times.

The team led by Murat Yücel say although modest use may not cause significant neurotoxic effects, the results suggest that heavy daily use might be toxic to human brain tissue.

The researchers say when it came to tests of verbal memory - recalling a list of 15 words - the marijuana users also had lower scores; they were also found to be more likely to have mild signs of psychotic disorders such as schizophrenia and mania.

The scientists say their findings challenge the widespread belief that marijuana has a limited or no harmful effects on the brain and behaviour and they suggest scans on larger numbers of people are needed to confirm the extent of the effect.

The scientists suggest that everyone is vulnerable to potential changes in the brain, some memory problems and psychiatric symptoms if they use marijuana heavily for long periods.

Groups campaigning for the decriminalisation of marijuana say the findings are misleading because they are based on men who were heavy, long-term users and say little about the vast majority who are moderate or occasional users.

They say the documented damage caused by the heavy use of alcohol or tobacco is far more serious, and high-tech scans are not needed to establish this.

The researchers have begun new research on the effects of both short-term and long-term and moderate and heavy use of marijuana.

The study is published in the American Medical Association's journal Archives of General Psychiatry.