Category Archives: Neuropsychological Batteries

Cannabis and Brain Damage: Neuropsychological Testing

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 EEG testing of cannabis users to discover evidence of brain damage, see here.

For an analysis of studies looking at cerebral blood flow in cannabis users, 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.

One of the ways of determining brain damage from the use of drugs is to subject users to neuropsychological batteries. A neuropsychological battery is a test that is specifically designed to pick up brain damage. This post will deal with the results of neuropsychological batteries of cannabis users.

Recent studies looking at various neuropsychological batteries have in general not shown any permanent brain damage from the long-term use of marijuana. According to Harrison Pope, a meta-analysis of such studies on long-term marijuana users found no brain damage in seven of the eight areas and only a small effect on the remaining area, learning.

Another meta-analysis of fifteen such studies of long-term users done by Igor Grant, who has been working in this area for a long time, concluded that marijuana did not cause brain damage. They did, however, find a “very small” impairment in learning and memory, but apparently did not feel it was significant enough to warrant being called brain damage.

A typical study, here, found deficits in current users, but none in former users, half of whom had been smoking 5 or more joints a week. The abstinence period was three months.

A study of male identical twins from the Vietnam Era, one of whom had formerly used marijuana and another of whom did not, found an absence of marked effects on cognition. A Canadian study found no permanent lowering of IQ scores in former heavy cannabis users.

Nevertheless, it also found that smoking more than 5 joints a week lowered one’s IQ by about 4.1 points. But smoking 3 joints a week or less raised IQ by 2-6 points, the same as abstaining from marijuana. The test measured IQ taken between ages 10-19, and the IQ rise was a consequence of going through adolescence.

Yet another study found that varying degrees of marijuana use from light to heavy did not accelerate cognitive decline in a group of 1200 persons of all ages. The only thing that did accelerate cognitive decline in this group was increasing age. Cognitive decline began as early as the 30’s and accelerated markedly in the 60’s.

Although permanent effects are dubious, there are residual effects for heavy users on memory, learning and recall. These effects are quite clear even 24 hours after use and in daily users, last, subtly, for up to a week after use and may be related more to a mild withdrawal syndrome, since they peak at about 3-5 days post-use. By one month post-use, though, these deficits are gone.

Therefore, chronic heavy users will always be somewhat impaired in these areas as long as they are using marijuana.

A 1995 study by Harrison Pope tested chronic heavy cannabis users against controls after one, seven and 28 days abstinence. Effects were seen at one and seven days, but after 28 days, there were virtually no differences between the groups.

This study shows that heavy long-term users will still be impaired even a week after their last joint. Yet it also shows that impairments are related more to recent use than to permanent damage.

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Filed under Cannabis, Dope, Hallucinogens, Intoxicants, Neuropsychological Batteries, Reposts From The Old Site, Science

Cannabis and Brain Damage: Summary

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 analysis of studies looking at cerebral blood flow in cannabis users, 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.

Original monkey and later rat studies indicating structural brain damage have generally not panned out when conducted in humans, but a recent study from 2008 found damage to the hippocampus and amygdala. The hippocampus findings are contradicted by three earlier studies finding no damage, and the finding on the amygdala was contradicted by an earlier study.

Another study found damage to the corpus callosum in early adolescent users. And another found damaged axons and brain cells in the prefrontal cortex. These findings have not yet been replicated. Yet another study found damage to two areas but improvements in four other areas of the brain. The consequences of this are not known.

At the moment, whether or not cannabis causes structural damage or even improvements to the limbic system, corpus callosum, prefrontal cortex or other areas of the brain is somewhat up in the air.

Neuropsychological studies of long-term users have been somewhat contradictory, but in general have not found significant brain damage, although they did find a “very small effect” on learning and memory. Apparently they did not think it was significant enough to be called brain damage.

New studies show that chronic long-term users perform worse than controls in memory, learning and recall, and the effect worsens as use progresses. These effects last up to one week after the last use. Therefore, daily marijuana users are always going to be somewhat impaired in these areas.

Some EEG studies found some interesting changes in theta waves in users who had used heavily and daily for 15-30 years. The significance of these findings is not yet known; one suggestion that is that the increased theta may be indicative of organic damage. But here again we do not have any clinical correlates of the organic theta change either.

Even this study did not find permanent effects from sporadic or occasional use of marijuana.

Another found problems with screening out external stimuli after five years of use, but it is possible that two attempts to replicate that study may have failed.

A SPECT studies out of Britain showed low CBF in three heavy cannabis users. Another found that low CBF did not clear up in adolescent users even after one month. However, they have been contradicted by two other studies, one showing that the CBF deficits clear up after three months, and another showing increases in CBF as opposed to decreases.

A new study using DTI found damage to the left side of the arcuate fasiculus in adolescent heavy cannabis users. This is one of the most disturbing findings to date, and adds weight to evidence that cannabis should not be used by adolescents, since the arcuate fasiculus is still developing in early adolescence. Nevertheless, no clinical significance has yet been attached to this finding.

But another DTI study looking at the entire brain found no evidence of generalized damage, and if anything, found that teenage cannabis users have less brain atrophy and more brain cells than non-users. We would expect a clinical correlate of this to be more intelligent teenage potheads, but no one is suggesting that.

Unless clinical correlates can be discovered, all findings of damage or enhancement of the brain via marijuana should be viewed with a critical eye.

So the evidence on permanent brain damage from long-term heavy marijuana use is rather contradictory and is still somewhat up in the air.

It looks like cannabis can be used for up to five years, or possibly up to 15 years, even on a daily basis, without any permanent harm to the brain. Beyond that, there may effects, but they appear to be more subtle than profound.

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Filed under Cannabis, Dope, EEG, Hallucinogens, Neuroimaging, Neuropsychological Batteries, Neuroscience, Reposts From The Old Site, Science