Starting marijuana before age 16 may hinder brain development

While starting marijuana at the age of 16 or younger may hinder brain development, using marijuana after age 16 can lead to accelerated brain ageing, warns a new study.

The findings suggest that the age at which an adolescent begins using marijuana may affect typical brain development.

"Science has shown us that changes in the brain occurring during adolescence are complex. Our findings suggest that the timing of cannabis use can result in very disparate patterns of effects," explained principal investigator Francesca Filbey from The University of Texas at Dallas, US.

The research team analysed MRI (magnetic resonance imaging) scans of 42 heavy marijuana users -- twenty participants were categorised as early onset users with a mean age of 13.18 and 22 were labelled as late onset users with a mean age of 16.9.

According to self-reports, all participants, aged 21-50, began using marijuana during adolescence and continued throughout adulthood, using cannabis at least one time per week.

The researchers found that the participants who began using marijuana at the age of 16 or younger demonstrated brain variations that indicate arrested brain development in the pre-frontal cortex, the part of the brain responsible for judgment, reasoning and complex thinking.

Individuals who started using marijuana after age 16 showed the opposite effect and demonstrated signs of accelerated brain ageing.

"Not only did age of use impact the brain changes but the amount of cannabis used also influenced the extent of altered brain maturation," Filbey noted.

The study was published in the journal Developmental Cognitive Neuroscience.