Monday, April 28, 2014

Brain abnormalities caused by marijuana use.

Numerous studies have shown that cannabis use is associated with impairments of cognitive functions, including learning and memory, attention, and decision-making. Animal studies show structural changes in brain regions underlying these functions after exposure to Δ9-tetrahydrocannabinol (THC). Now, a sobering bit of information on structural changes in human brains from Gilman et al.:
Marijuana is the most commonly used illicit drug in the United States, but little is known about its effects on the human brain, particularly on reward/aversion regions implicated in addiction, such as the nucleus accumbens and amygdala. Animal studies show structural changes in brain regions such as the nucleus accumbens after exposure to Δ9-tetrahydrocannabinol, but less is known about cannabis use and brain morphometry in these regions in humans. We collected high-resolution MRI scans on young adult recreational marijuana users and nonusing controls and conducted three independent analyses of morphometry in these structures: (1) gray matter density using voxel-based morphometry, (2) volume (total brain and regional volumes), and (3) shape (surface morphometry). Gray matter density analyses revealed greater gray matter density in marijuana users than in control participants in the left nucleus accumbens extending to subcallosal cortex, hypothalamus, sublenticular extended amygdala, and left amygdala, even after controlling for age, sex, alcohol use, and cigarette smoking. Trend-level effects were observed for a volume increase in the left nucleus accumbens only. Significant shape differences were detected in the left nucleus accumbens and right amygdala. The left nucleus accumbens showed salient exposure-dependent alterations across all three measures and an altered multimodal relationship across measures in the marijuana group. These data suggest that marijuana exposure, even in young recreational users, is associated with exposure-dependent alterations of the neural matrix of core reward structures and is consistent with animal studies of changes in dendritic arborization.


  1. Anonymous9:48 AM

    I am now lost...
    Is this mean, THC makes more Gray-Matter (Neurons) in those areas, without losing Gray-Matter from the rest?

    Dr.Bownd, Can you please upload the full-text article or HQ MRI scans here if you have access? Thanks

  2. About the media coverage of that study :
    Study of Pot Smokers' Brains Shows That MRIs Cause Bad Science Reporting

  3. If you will send me your email address, I can send you a PDF of the article.

  4. Anonymous11:38 AM

    I've found the article's PDF version at

    It does not support an idea of Neurogenesis caused by THC at those areas, except hippocampus though, but a matter of neuroplasticity caused by differences in life-style, maybe? 20n subjects sure isn't enough to make rightful conclusion.