Long-term cannabis use ‘changes brain structure and leaves users demotivated, unable to make decisions and struggling to deal with complex tasks’

Long-term cannabis use changes the structure of the brain and leaves users demotivated and unable to make decisions, a study suggests.

Cannabis can be legally prescribed in Britain for some medical conditions and is often viewed as low-risk or harmless by recreational users.

But researchers from Fidmag Germanes Hospitalàries Research Foundation in Spain found extended use is linked to ‘thinning’ in the frontal cortex of the brain.

Thinning in this area, which is involved in high-level planning and executive function, could mean a loss or shrinkage of important brain cells, or fewer connections between those cells.

Leader author Ana Aquino-Servin said the findings mean that regular, heavy users of cannabis may find it hard to be motivated to do complex tasks.

She told The Times: ‘Executive functions are really complex processes and it includes planning, decision making, working memory.

‘They are processes that we need every day to deal with daily problems.

“Maybe they [regular cannabis users] don’t have a big struggle to do [tasks], but maybe the brain needs to do more work to do it.

‘We can probably find degrees in productivity, also, in doing work tasks.

‘I think another issue that can be going on here is the relation between [cannabis] use and a decrease of motivation.

‘There’s some evidence that cannabis users have less motivation, so this can also lead to a reduction of starting tasks.’

More research is needed to establish whether these changes are permanent and definitively caused by cannabis or if they would eventually reverse after cannabis use stopped.

Green Party leader Zack Polanski is among those campaigning for the legalisation of cannabis, arguing this would allow for better regulation and revenue from taxation.

But scientists have warned that more research may be needed to understand the long-term effects of the drug use before the substance is further legalised.

The study, presented at the European Congress of Psychiatry in Prague, examined 46 adults who had reported that they had been using cannabis for an average of a decade, and had used it daily for at least five years.

These adults, who had an average age of 31, were given MRI scans, which were compared with an equal number who had used cannabis fewer than ten times over their lifetime.

The analysis revealed the brain was thinner in the right rostral middle frontal cortex in people who had smoked cannabis daily for at least five years.

Previous research has shown that cannabis use can affect the frontal lobe in young adults and teenagers, but this study is one of the first to report structural differences associated with long-term daily use in adults.

Researchers believe the high number of CB1 receptors, which bind to the main psychoactive compound in cannabis to produce a ‘high’, in the frontal lobe cortex may explain why this area is more affected by sustained use.

Dr Julian Beezhold, the secretary general of the European Psychiatric Association, said: ‘As cannabis policies and public attitudes evolve, robust imaging studies like this are important for informing public health discussions with objective data.’