And, those who start after 16 have accelerated brain aging, study says

That's the part of the brain responsible for judgment and reason

Those who start under 16 don't have fully formed prefrontal cortex

Cannabis has long-term effects on a person’s brain – especially if they start using the drug earlier in life, according to a new study.

Starting to use marijuana before the age of 16 has been found to result in an underdeveloped prefrontal cortex, scientists revealed.

That’s the part of the brain responsible for judgment, reason and complex thinking.

In contrast, people who start to use marijuana after the age of 16 experience accelerated brain aging.

Lead study author Dr Francesca Filbey, of the University of Texas at Dallas, said: ‘Not only did age of use impact the brain changes but the amount of cannabis used also influenced the extent of altered brain maturation.’

Marijuana can have long-term effects on a person's brain, regardless of when they start using the drug, scientists revealed. The earlier a person starts smoking, the more significant the damage, a study said

A team of researchers from the university’s Center for BrainHealth analyzed MRI scans of 42 heavy marijuana users.

Each of the participants were between the ages of 21 and 50, and indicated that they began using cannabis in adolescence.

All of the participants continued to use marijuana through adulthood – using the drug at least one time each week.

Twenty of the study’s participants were categorized as early onset users – with a mean starting age of nearly 14.

Additionally, 22 of the participants were found to be late onset users – with a mean starting age of nearly 17.

Typically, in adolescent brain development, the brain prunes neurons – resulting in reduced cortical thickness, as well as a greater amount of gray and white matter contrast.

Pruning usually leads to increased gyrification - the addition of wrinkles or folds on the surface of the brain.

Through MRI scans, the scientists determined that the more marijuana consumed by early onset users, the greater their cortical thickness.

Additionally, early onset users were also found to have less gray and white matter contrast, and a less intricate gyrification.

The scientists said these findings indicate that when the participants began using marijuana before age 16, their brain experienced arrested development in the prefrontal cortex.

As for those who started using marijuana after age 16, they were found to have brain changes that normally occur later in life.

People who start smoking before the age of 16 were found to have underdeveloped prefrontal cortex - which is the part of the brain responsible for judgment and reason. Conversely, those who started after age 16 had accelerated ageing in the brain. Pictured here, the effects of cannabis on the prefrontal cortex

Those people had thinner cortical thickness, as well as stronger gray and white matter contrast.

Dr Filbey said: ‘In the early onset group, we found that how many times an individual uses and the amount of marijuana used strongly relates to the degree to which brain development does not follow the normal pruning pattern.

‘The effects observed were above and beyond the effects related to alcohol use and age.

‘These findings are in line with current literature that suggest that cannabis use during adolescence can have long-term consequences.’

Dr Filbey added that a longitudinal study is needed to establish a causal relationship between brain alterations and marijuana use.