Chronic marijuana use may alter your brain

Cannabis is being legalised in many jurisdictions, but a new study raises concerns over long-term structural changes to the brain caused by the drug.

Long-term marijuana use may cause the brain to shrink, but also for it to increase its wiring to compensate – at least in the early stages – researchers have found.

They tested 48 users and 62 nonusers aged 20 to 36 and found that the marijuana users’ brains had lower volume of grey matter but more connectivity in the white matter. The marijuana users took the drug three times a day, on average.

It is one of the first studies of the effects of long-term usage of the drug and comes as laws against marijuana are being relaxed, particularly in the United States.

The brain scans of the subjects combined three different magnetic resonance imaging (MRI) techniques to evaluate brain characteristics.

“The results suggest increases in connectivity, both structural and functional that may be compensating for grey matter losses. Eventually, however, the structural connectivity or ‘wiring’ of the brain starts degrading with prolonged marijuana use," said co-lead author Dr Sina Aslan, from the University of Texas at Dallas.

The scans showed shrinkage in the orbitofrontal cortex (OFC) region of the brain in regular users who had used the drug for at least six years. The OFC is involved in decision making.

The study also showed a lowered IQ in regular cannabis users, but the researchers said this appeared to be unrelated to the changes in the brain structure.

Co-author Dr Francesca Filbey, also from the University of Texas, told reporters that the increase in connectivity may mask the shrinkage to the OFC and explain why chronic, long-term cannabis users appeared to be “doing just fine”.

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