Marijuana’s Effect on the Brain

New evidence suggests prolonged use of marijuana may lead to decreased brain volume. Surprisingly, marijuana also causes increased connectivity within the brain, as found by the Centre for Brain Health in the University of Texas, Dallas. Other studies have found reduced brain volume of this kind but this study is unique in its further findings about connectivity. Moreover, they found a correlation between these effects and age at first frequent use.

The study matched 48 regular users who used marijuana 3 times a day on average and 62 non-users for age and gender. MRI techniques were used to look at brain volumes and connectivity, in a study much more detailed and robust than any other.

While the orbitofrontal cortex, involved in decision making and emotion, had lower volume in users than non-users, there were increases in functional and structural connectivity, which they speculate may compensate for loss in brain volume.

However, after regular use for 6-8 years, connectivity began to degrade. Interestingly, there was an association between age at onset of regular marijuana use and overall increased connectivity. This was coupled with the finding that the greatest rate of increase in connectivity was found at the start of regular use. The researchers postulated that this indicated a highly complex relationship between cannabis use and long-term abnormalities in the brain involving a neuroadaptive process.

The studies call for more long-term research to answer questions about the effects for occasional users, or if the process can be reversed if regular users kick the habit.