FRIDAY, Jan. 6 (HealthDay News) -- Smoking marijuana can mean
different things to different people -- for some, anxiety and
paranoia can set in, while others mellow out.
Now, a unique brain scan study suggests two ingredients in pot
may work independently to achieve these effects.
British scientists who watched the effects of the two marijuana
ingredients -- Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD)
-- on the brains of 15 young men say the research shows how the
drug can either ease or agitate the mind.
"People have polarized views about marijuana," said study lead author Dr. Sagnik Bhattacharyya, a researcher in the department of psychosis studies at the Institute of Psychiatry, King's College London. "Some consider it to be essentially harmless but potentially useful as a treatment in a number of medical conditions, and others link it to potentially severe public health consequences in terms of mental health. This study explains why the truth is somewhere in between."
The findings were published in the January issue of
Archives of General Psychiatry.
According to Bhattacharyya's team, it's long been noted that
cannabis can prompt the onset of psychotic symptoms, such as
paranoia and/or delusional thinking, among otherwise healthy
"A number of studies have (also) clearly shown that regular marijuana or cannabis use in vulnerable individuals is associated with increased risk of developing psychotic disorders such as schizophrenia, where one loses contact with reality," Bhattacharyya said.
Just how this occurs in the brain wasn't understood.
In the new study, the researchers used functional MRI brain
imaging on 15 healthy men, roughly 27 years old on average and
described as "occasional cannabis users."
On three occasions under fMRI monitoring, the men received one
of three identical-looking gelatin capsules: one containing 10
milligrams (mg) of the marijuana ingredient THC (deemed to be a
"modest" dose); another containing 600 mg of CBD; and a third
filled with flour.
Testing was conducted in a highly controlled and monitored
environment, in which no marijuana was actually smoked.
The fMRI scans (which track brain activity in real time) were
conducted one and two hours after capsule administration. During
the scans, the men engaged in simple visual-cognition tasks (such
as pressing buttons to reflect the direction of a series of
flashing arrows). Psychopathological assessments were conducted
throughout the brain imaging process.
The team found that THC and CBD appeared to affect the brain in
different and opposite ways.
Ingesting THC brought about irregular activity in two regions of
the brain (the striatum and the lateral prefrontal cortex) that are
key to the way people perceive their surroundings. THC seemed to
boost the brain's responses to otherwise insignificant stimuli,
while reducing response to what would typically be seen as
significant or salient.
In other words, under the influence of THC, healthy individuals
might give far more importance to details in their environment than
they would have without the chemical in their brain.
THC also prompted a significant uptick in paranoid and
delusional thinking, the authors said, and the more that "normal"
brain responses were set off-kilter, the more severe the paranoid
or even psychotic reaction.
The effect of the other main pot ingredient, CBD, was nearly the
Ingesting the CBD capsule appeared to prompt brain activity
appropriate responses to significant stimuli in the
environment, the team reported.
According to Bhattacharyya, this suggests that, on balance,
marijuana may play both a good and bad role in the context of
The study also suggests that CBD, at least, may "have potential
use for the treatment of psychosis," he said, even as marijuana's
other principle ingredient, THC, raises the risk for developing
Dr. Joseph Coyle, a professor of psychiatry and neuroscience at
Harvard Medical School in Boston, said the current work goes a long
way toward "connecting all the dots" when it comes to understanding
the marijuana experience.
"What we're talking about here is the kind of perception, in this case prompted by marijuana, that leads a person to think that other people who are just talking in the subway are all actually talking about him," he noted. "Or people who are just tipping their hat for no reason are actually doing so specifically about him. And so this paper strikes me as important, because it actually looks at this kind of increased anxiety and increased hyper-alertness which are major factors in psychosis -- and then finds out what's going on in the brain among people who experience them.
"So I think this provides another brick in the foundation when talking about direct causality," he said. "It links the psychological state marijuana brings about with a specific psychophysical response in the brain. And that's very, very interesting."
There's more on marijuana at the
U.S. National Institute on Drug Abuse.
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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