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Does Long Term Marijuana Use Cause Brain Damage? New Study Finds Purported Link

According to a new study out of the Murdoch Childrens Research Institute there appears to be some credible link between long term usage of marijuana and brain damage.  We know, we know, this is something we have heard bandied around for a while now and every now again someone else shows some link which is countered later down the path.  This study is a little different however because it appears to be focused on white brain matter which is the first of its kind to do so.  At Live Rehab we like to take new studies with a little bit of skepticism before touting them as complete gospel and as such have a few questions which should rightly be answered about the methods and details.

One of the main issues we have with the study and lack of details surrounding their published work is the actual amount of heavy usage.  What they consider heavy usage might be incredibly high and dangerous compared to small occasional users.  Additionally there is not a mention of what age the study used to conduct the research.  While we are sure that they did take these factors into consideration, the media has taken this headline and sensationalized it without asking the pertinent questions. If long term marijuana usage causes brain damage, as their study indicates, we need to know what the circumstances are so that the rehab community can appropriately adjust our approaches.  We have reached out to the Murdoch Childrens Research Institute for clarification on these points and will post an update when/if we receive a response.  The full report, for those with access to the Brain journal is located here


The media contact for the Institute has provided us with a full copy of the study which we will evaluate and hopefully have our questions answered.  According to the full study the users consumed large amounts, on average 147 joints per month and typical long term usage was around 15 years.  Furthermore there is very little cross drug usage/experimentation which is good since it solely focuses on the effects of the marijuana (not including alcohol).

Journal Abstract:

Cannabis use typically begins during adolescence and early adulthood, a period when cannabinoid receptors are still abundant in white matter pathways across the brain. However, few studies to date have explored the impact of regular cannabis use on white matter structure, with no previous studies examining its impact on axonal connectivity. The aim of this study was to examine axonal fibre pathways across the brain for evidence of microstructural alterations associated with long-term cannabis use and to test whether age of regular cannabis use is associated with severity of any microstructural change. To this end, diffusion-weighted magnetic resonance imaging and brain connectivity mapping techniques were performed in 59 cannabis users with longstanding histories of heavy use and 33 matched controls. Axonal connectivity was found to be impaired in the right fimbria of the hippocampus (fornix), splenium of the corpus callosum and commissural fibres. Radial and axial diffusivity in these pathways were associated with the age at which regular cannabis use commenced. Our findings indicate long-term cannabis use is hazardous to the white matter of the developing brain. Delaying the age at which regular use begins may minimize the severity of microstructural impairment.

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Aug 12, 2012

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