Evidence shows heavy marijuana use may harm the brain

Heavy marijuana use has been linked to adverse changes in the function and structure of areas of the brain associated with reward, decision making and motivation, according to researchers at the Center for BrainHealth at The University of Texas at Dallas.

Findings show that heavy or chronic users (people who use marijuana at least four times per week in a six-month period) have smaller brain volume in the orbitofrontal cortex (OFC), or the part of the brain commonly associated with addiction, in addition to increased brain connectivity.

According to the authors, this could be a compensation for grey matter losses. Findings also show that severity of use directly correlates to greater connectivity.

These findings were more pronounced in those who started using marijuana at a young age, indicating the damaging effects of long-term use as well as the increased vulnerability of a developing brain.

Although structural wiring was found to decline with prolonged chronic use over six to eight years, marijuana users continued to display more intense connectivity than healthy non-users. This could explain why chronic, long-term users are seemingly fine, despite smaller OFC brain volumes, according to the authors.

Further studies are needed to determine whether:

• Changes revert back to normal with discontinued use;
• Similar effects are present in occasional marijuana users versus chronic users; and
• The effects are indeed a direct result of marijuana use or a predisposing factor.

Research was funded by the National Institute on Drug Abuse.