Marijuana On The Brain

When scientists presented data from a new study at the 2nd International Cannabis and Mental Health Conference showing brain changes when patients ingested THC, anti-weed heads claimed it was physical proof cannabis has damaging effects on the brain.

The media freaked out in May when it reported on new research that provided physical evidence of the “damaging effects” of cannabis on the brain.

What happened is that scientists presented data from a new study at the 2nd International Cannabis and Mental Health Conference in London, UK. Phillip McGuire and colleagues at King’s College London gave subjects THC and cannabidiol (CBD), two of the active ingredients in cannabis, and then stuck them in MRIs to take pictures of their brains’ reaction to the drugs.

The CBD calmed down the amygdala, effectively reducing any fear patients might have experienced while looking at pictures of anxious faces. The THC affected several regions of the brain, including the inferior frontal cortex, which controls psychotic episodes.

Anyone who has smoked pot knows that hallucinations and paranoia are common side effects. So the fact that THC lit up the paranoia region in brain scans is hardly earth-shattering. The problem is in how these results were reported by the media.

Brain scans only capture a moment in time. In this case, a moment when the brain was high. To say that the scan represents evidence of damage is misleading. “It’s important to note when covering brain scan-based research that a ‘change’ in the brain isn’t necessarily a bad thing: learning, falling in love, seeing, hearing and virtually any other experience can be expected to cause changes in the brain,” says Maia Szalavitz, senior fellow at, a media watchdog group. “The tricky part is determining what brain changes mean.”

The study is the first to map the regions of the brain affected by CBD and THC and that makes it interesting. It could lead to the development of drugs targeting specific brain regions. To imply that it proves that THC damages the brain reads far more into the results than the science can support.

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