Cannabis and Brain Damage: Cerebral Blood Flow Findings

Repost from the old site.
The original post in its native form was far too long, so I have decided to break it up into seven different posts, in addition to this post. The separate sections are listed below.
The original post, what is left of it, is here.
For an examination of the evidence of whether or not cannabis causes actual structural damage to brain cells, axons or dendrites, see here.
For an analysis of neuropsychological batteries of cannabis users to determine whether or not they suffer brain damage, see here.
For an analysis of EEG testing of cannabis users to discover evidence of brain damage, see here.
For an admittedly impressionistic analysis of whether or not cannabis causes schizotypal symptoms in users, see here.
For a summary comparing the effects of cannabis on the brain compared to other drugs, see here.
For a summary of the findings of cannabis and brain damage, see here.
With the use of SPECT and MRI, we can now measure changes in blood flow in various parts of the brain. Permanent changes in blood flow, especially low blood flow, are said to be indicative of brain damage.
Recently, some new SPECT studies have come out of Britain, and were published in the Journal of Psychoactive Drugs, appearing to show reduced CBF activity in certain areas of the brain with long-term heavy use of “skunk weed”, which is extremely potent marijuana. However, the part in the article where they talk about a user’s brain being “pitted and scarred” is nonsense. These are just areas of reduced activity.
One user was a 16-year-old who had smoked every day for two years, another an 18-year-old who had smoked several times a week for two years and the third was a 28-year-old who had smoked for 10 years.
Whether or not areas of reduced activity can be said to be “damaged” is an extremely difficult proposition to make. If the reduced activity is permanent, we can say that, but if it is temporary, it’s simply not “damage.”
A report also indicated that a similar study showed an effect even after one month post-use in teenagers.
Another study, this time using MRI to look at cerebral blood flow, actually found increased blood flow in the right frontal lobe, left temporal lobe and the cerebellum in chronic, long-term daily cannabis users. This means increased activity in these areas.
If the British study is being used to say that cannabis damages the brain on basis of low cerebral blood flow, then this study can be used to say that cannabis improves the brain based on cerebral blood flow. Furthermore, this study would seem to contradict the British study.
Yet another study concluded that very heavy cannabis use may be harmful, while more moderate or light use may be less deleterious. This study found that perfusion deficits in cerebrovascular flow attenuated in light to moderate users after one month’s absence, while persisting in heavy users. Moderate use was defined as 2.5-10 joints/day, while heavy use was defined as 11-50 joints/day.
This study completely contradicts the British study that got so much media attention.
The CBF findings may be related to dose. One study found an effect at 7.5 joints+/day, but found no effect at 5 joints/day or less. According to this study, it would be prudent to limit oneself to 5 joints a day or less.
The finding of this study, of reduced activity in the frontal cortex combined with increased activity in the cerebellum, is a fairly common one in recent studies. Rather than damage, this appears to be a neuroadaptation to the effects of cannabis use on the brain.
Yet another CBF study found changes in CBF in abstinent cannabis users on a stroop test. They found low CBF in the left perigenual anterior cingulate cortex and the left lateral prefrontal cortex and excessive flow in the hippocampus. The two regions with low blood flow are said to be involved in something called executive function, which I do not completely understand.
The cannabis users scored the same as controls on the stroop test, but they used a different brain style than the one people typically use to  complete the test. Since the scores were the same, the significance of this study is called into question.
There is an increasing body of literature showing that cannabis users utilize alternate brain networks than those normally employed, possibly to compensate for the effects of cannabis.

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7 thoughts on “Cannabis and Brain Damage: Cerebral Blood Flow Findings”

  1. This stuff you talk of is bunk science. It is 100% unproved. Welcome back to the age of snake oil.
    And anyway from the perspective of legalization it’s irrelevant. Marijuana has been illegal for seventy years and in all that time it’s been widely used. We didn’t substitute the harms of the prohibition for those of marijuana, we lumped the harms of the prohibition right on top of those of marijuana! The prohibition caused more than 6,000 cartel murders last year and will cause at least 7,000 this year. The “brain damage” you speak of caused none.
    When we legalize the production and sale of marijuana to adults we’ll give ourselves the power to undercut cartel prices, thus stripping them of their customers and eliminating their marijuana incomes. According to the ONDCP the cartels make $8 – 10 BILLION a year from selling marijuana in the U.S. – this amounts to two-thirds of their incomes. By eliminating this income we’ll decimate them and end their ability to continue killing children, police officers and politicians.
    And the “harms” of marijuana that you speak so urgently about – we’re already living with them. 100 million Americans have obtained and consumed marijuana during the prohibition, more than 6,000 people in this country use marijuana for the first time every single day.
    We will *always* have marijuana in our society, but we don’t always need to have the prohibition.

    1. Hi. I’m a cannabis user myself, and have been involved with the marijuana legalization movement since 1980. I know Alan St Claire and Dale Geiringer. I knew Gordon Brownell. I know Lester Grinspoon. Alan said that out of all the laypeople he had ever met, I knew more about pot than any of them, except for some guy in Alaska. I know what I’m talking about.
      I’m a user myself, BTW.

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