Marijuana users who had smoked more than 5 joints a day (average of 11 joints a day) for more than 10 years (average use of 20 years) were tested.
They found that there was shrinkage in the amygdala and the hippocampus related to how much cannabis the person used.
The shrinkage was not large in either structure. The damage is described as "equivalent to mild traumatic brain injury or premature aging." The article:
Doctors have known for years there is nothing "soft" about the drug cannabis. Professor Jon Currie is the director of addiction medicine at St Vincent's Hospital in Melbourne.
"This is a very exciting study because it proves for the first time what we have been really worried out. That brain problems are real and that people who smoke cannabis over a long term do get problems." he said.
It's also equivalent to drinking over 2 drinks per day. It's equivalent to severe stress. It's equivalent to having PTSD. It's equivalent to all sorts of stuff.
This study was done by Nadia Solowij out of Australia. For whatever reason, every single study done by Solowij and colleagues seems to find pretty serious brain damage.
This study is pretty scary, but so far there have been four other studies of heavy cannabis users that did not find damage to the hippocampus or the amygdala.
However, four other studies found no hippocampal damage from cannabis. An MRI study from 2005 of very heavy cannabis users who had used cannabis on average of 20,100 times found no damage to the hippocampus at all. A study of cannabis-using young adults from 2006 found no damage to the hippocampus, or to any other structure. And a third study also found no hippocampal damage.
The study of users from 2006 also found no damage to the amygdala. This study actually found that the hippocampus-amygdala was 5% larger in the cannabis users than in the non-users, but the difference was not thought to be significant.
So there you have it. There are some pretty scary new findings coming out about cannabis and damage to the limbic system, but things are still far from proven. The single study so hyped by the media nowadays has already been contradicted by four negative studies. You would think that the media might have noted that. You would think wrong.
The road forward? More studies, I guess. You could always try smoking less than five joints a day too, just to be on the safe side.
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The latest death toll figures from Hurricane Katrina can be seen on this website here. The famous Russian neo-Nazi video is on this blog here.
Updated August 23:
The original post in its native form was far too long, so I broke it up into seven different posts, in addition to this post. The separate sections are listed below.
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 of the findings of cannabis and brain damage, see here.
LSD and psilocybin, while not causing permanent brain damage (that we know of so far), can cause HPPD (Hallucinogen Persisting Perception Disorder), a long-term perceptual disturbance of unknown etiology.
I have HPPD myself from using hallucinogens about 40 times, but "suffering" from HPPD once again is an interesting concept, at least in my case.
All I get are brighter colors, mostly in neon signs and store displays, and only at certain times. Maybe lots of people would love to have this effect, as the world looks so much better this way. I called up an ophthalmologist about it and he laughed me off the phone, saying he doesn't treat people whose colors improve. It is only my continuing neurosis that causes me to view these changes as frightening instead of integrating them.
LSD does have a deleterious effect on the visual system of the brain - it is hypotoxic to that area in lab animals, for instance, birds - but it doesn't cause any generalized brain damage at all that we know of, and we have been studying LSD's effects on the brain for about 50 years or so now.
LSD does cause reductions in 5-HT2 receptors on serotonin neurons. But this is a case of these receptors retreating back into the cell due to LSD's assault on those receptors. After about a week, the receptors to poke back out of the cell again.
The most recent evidence also indicates that psilocybin (mushrooms) and mescaline (peyote) also do not cause any generalized brain damage, although psilocybin can cause HPPD. Due to the risks of HPPD, this blog unfortunately does not recommend that anyone use LSD or psilocybin even one time, unless maybe if you are dying.
Ecstasy (MDMA) produces comparatively dramatic harm to the brain after only a handful of doses (2-10 doses), with the effects increasing with continued use. The drug causes degeneration of serotonergic axonal terminals, which afterwards do not grow back correctly, if at all.
There are suggestions that there may be hippocampal damage. On intelligence tests there are deficits in working memory, declining vocabulary, impairments in verbal learning, associative learning and attention and increased distraction. There also seem to be some mood changes.
Therefore, it appears that using Ecstasy one time is possibly safe. However, taking Ecstasy as few as an average of 3.2 times causes noticeable damage in verbal memory. Ecstasy should be taken no more than once in a lifetime, if at all.
Evidence strongly suggests that the heavy use of PCP, ketamine and DXM may cause permanent brain damage and can often cause schizophrenia-like symptoms which may be related to that damage. The theorized damage involves the vacuolization of neurons (basically a hollowing out and death of the neuron) in various parts of the brain.
The evidence comes from rat studies and the dosages have been criticized, but humans are far more sensitive to the effects of dissociatives than rats are, so the differential doses are probably about right.
The rat evidence has now been challenged by monkey studies, so the matter is far from settled. But until it is, extreme caution, if not outright avoidance, seems to be the best policy for these drugs.
PCP can probably be used up to a dozen or so times in life with no permanent damage. Beyond that, things get a lot touchier. Heavy users show an extremely high rate of schizophrenic and psychotic symptoms, along with symptoms of brain damage. There seems to be some recovery with abstinence, but full recovery is by no means assured.
Evidence indicates that ketamine can be used at least once with no permanent consequences at all to the brain. Beyond that, it is up in the air. Ketamine can surely be used at least a dozen times with no risks to the brain. Beyond that, things get hazier.
Heavy DXM users have reported a very high rate of psychosis and schizophrenia-like symptoms, along with symptoms of organic brain damage. Users should approach DXM use with caution, and heavy use should be ruled out.
Heavy methamphetamine use has been proven to cause permanent damage to dopaminergic systems, especially in the striatum, caudate and putamen (at 1/2 gram a day, 5 days a week, and 2 years of use). Studies have also shown degeneration of axons on serotonergic neurons and loss (cell death) of up to 15% of the neurons of the hippocampus with heavy use.
In the study above, there was some recovery of the dopaminergic system with abstinence, but it was only partial. Meth can probably be used a dozen or so times without any permanent damage. Beyond that, no guarantees. There is some suggestive evidence of chronic psychosis, depression and anxiety directly related to heavy methamphetamine use (over 10 years of heavy use).
Impairments in learning, processing speed, and working memory, along with delayed recall, are found in meth users. Brain dysfunction is often readily apparent in heavy meth users. This is one category of drug user, in contrast to most other drug users, that does sometimes appear "fried". Much of this "fried" appearance seems to clear up with abstinence.
Methamphetamine can probably be used up to a dozen times or so in moderation without any permanent consequences to the brain. Nevertheless, some users have reported permanent effects from only 2-3 weeks of very heavy use. Meth is nasty stuff, and it's best to keep away from it.
Heavy drinking can depress neurons for up to two years. With continued heavy drinking, at some point, there is organic damage, which in many cases is permanent, although there is often significant recovery with abstinence. The case of the "wethead" and "dry drunk", the former alcoholic who is still damaged, psychologically or cognitively, is well known.
Heavy use of barbiturates over many years causes a damage syndrome that looks like chronic alcoholism and that does not completely recover with abstinence.
Even chronic Valium use causes long-term EEG changes of unknown significance.
Sniffing glue has been proven to be possibly the worst thing you can do to your brain short of putting a bullet in it, and the effects do not recover completely with abstinence.
Cocaine, unfortunately, seems to be capable of causing brain damage with as few as 11 doses (constriction of vessels in the brain). At three years of using several times a week, there is slowing on the P300 event related potentials test, that may not recover fully with abstinence.
Recent studies have also shown that chronic heavy cocaine use causes reductions in gray matter in various parts of the brain. This means that heavy cocaine use causes an actual loss of brain cells in parts of the brain. It may also cause white matter reductions, which means a loss of connections in the brain.
This blog recommends that lifetime use of cocaine be limited to 10 times or less. Even there, there is a slight risk of sudden death due to perturbations in the heart's electrical rhythms. These perturbations can cause a sudden heart attack or even possibly a stroke. Vasoconstriction is probably involved.
In many of the above cases, there is some recovery with abstinence, but often not to the previous level.
Experimental use of PCP, ketamine, cocaine and methamphetamine (use up to a dozen or so times for each one) probably does not cause significant permanent damage. Beyond that, you play with matches.
Compared to other drugs of abuse, such as Ecstasy, PCP, Ketamine, DXM, cocaine, methamphetamine and alcohol, the effects of cannabis on the brain are dramatically less deleterious.
In terms of its effects on the brain for heavy users, cannabis is surely by far least damaging intoxicant of them all, for what that is worth.
Note: Readers should carefully read the Commenting Rules before commenting to avoid having their comments edited or deleted and to avoid being banned from the site.
The latest death toll figures from Hurricane Katrina can be seen on this website here. The famous Russian neo-Nazi video is on this blog here.
Updated August 23:
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.
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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Independent Left journalist in California. Trustafarian in a shackteau, slumming it up in the barrio. Revolutionary, Leftist nationalist, Christian, liberation theology, replacement theology. BA Journalism, MA Linguistics, Green Party, Communist Party USA, Democratic Party.
Generally, topics focused through a progressive yet heterodox lens. Discusses race a lot. Also lots of shock and horror videos - if it bugs you, don't read or watch. Pan-humanist universalist, non-racist race realist, despises the PC, Cultural Marxist, Identity Politics, Western New Left. Iconoclast, smashes all party lines, angers everyone. Notorious provocateur; if I'm not making you mad, I'm not doing my job. Channeling Andy Kaufman, Tony Clifton, Lenny Bruce, Ambrose Bierce, Mark Twain, H.L. Mencken, Kinky Friedman, Hunter S. Thompson and Wally Gator. Shoot first.
