Cannabis and the brain

In Progressives Should Just Say No to Legalizing Drugs (US News), Carrie Wofford writes, “There’s a good reason drugs are illegal: They’re dangerous”.

She explains:

Drugs kill. They turn talented, intelligent people into impulsive animals. They destroy marriages. They deprive children of emotionally healthy parents. There’s a good reason drugs are illegal: They’re dangerous. Products that kill do not belong on drugstore shelves.

After reminding the reader of Philip Seymour Hoffman’s tragic overdose (whose heroin addiction was the result of legal drugs prescribed to him for pain), Wofford brings Cannabis into the argument by citing its deleterious effects on brain tissue:

Even the least damaging drugs – like marijuana – still kill brain cells and even shrink parts of the brain with prolonged use. Proponents argue that marijuana is no worse than tobacco, which is available on drugstore shelves… While tobacco is addictive and causes many health problems (draining public health resources), cigarettes don’t shrink parts of the brain. Why would we want a generation of teenagers to have smaller brains with fewer brain cells from smoking marijuana?

A few points:

  • Cigarettes don’t just drain public health resources and cause “health problems”, they end lives at the rate of 1,300 deaths DAILY in the US. It would seem that after dying from cigarette smoking, the size of one’s brain would be of little importance.
  • The author gives no reference for her claim that Cannabis kills brain cells. She leaves a reference to “WebMD” which discusses a study involving 25 individuals and is peppered with phrases like  “these results suggest” and “associated with”, and says there is conflicting evidence.

In the study, researchers used high-resolution magnetic resonance imaging to compare the brain structure of 15 men who smoked more than five joints of marijuana daily for more than 10 years with images from 16 men who did not smoke pot…The results showed men who smoked pot regularly had significantly lower brain tissue volumes in the hippocampus and amygdala areas.

To investigate CNS effects of frequent marijuana use, brain tissue volume and composition were measured using magnetic resonance imaging (MRI) in 18 current, frequent, young adult marijuana users and 13 comparable, non-using controls. Automated image analysis techniques were used to measure global and regional brain volumes, including, for most regions, separate measures of gray and white matter. The marijuana users showed no evidence of cerebral atrophy or global or regional changes in tissue volumes. Volumes of ventricular [ cerebrospinal fluid] were not higher in marijuana users than controls, but were, in fact, lower. There were no clinically significant abnormalities in any subject’s MRI.ue volumes in the hippocampus and amygdala areas.

Researchers scanned the brains of 92 adolescents, ages 16 to 20, before and after an 18-month period. During that year and a half, half of the teens — who already had extensive alcohol and marijuana-use histories — continued to use marijuana and alcohol in varying amounts. The other half abstained or kept consumption minimal, as they had throughout adolescence. The before-and-after brain scans of the teens consuming typically five or more drinks at least twice a week showed reduced white matter brain tissue health…However, the level of marijuana use — up to nine times a week during the 18 months — was not linked to a change in brain tissue health

There is evidence that shows Cannabis may grow brain cells, may protect the brain, and that it shrinks cancerous tumors and heals damage caused by chronic stress:

The following from WIRED Science:

Does Marijuana Make You Stupid?

Marijuana is currently regulated by the United States government as a Schedule I drug, placing it in the same category as heroin, MDMA and LSD. This is largely due to the first condition of Schedule I drugs, which is that the substance “has a high potential for abuse.” The language in that clause is deliberately vague. Does abuse equal addiction? Probably not, since marijuana is not addictive like other Schedule I drugs. Rats don’t self-administer the compound in a lab, it’s virtually impossible to fatally overdose on the drug, and the physiological effects of marijuana withdrawal, if they occur, are far milder than those experienced by chronic amphetamine, alcohol, nicotine or opiate users. Put another way, if “abuse” means “addiction” then cigarettes should be Schedule I, not marijuana.

Rather, the case for marijuana “abuse” has always stemmed from its cognitive effects. While cigarettes are like caffeinated smoke — they increase attention and productivity, marijuana is the drug of choice for slackers, hippies and Seth Rogen characters. In popular culture, all it takes is one hit from a bong before people become ridiculously dumb, unable to solve the simplest problems or utter a coherent sentence. Potheads eat a lot and laugh at stupid jokes. The larger worry, of course, is that such damage is enduring and that “smoking dope” permanently impedes learning and memory.

That, at least, has been the collective stereotype for decades. There’s even been some science to back it up, especially when the marijuana use begins at an early age. But now a different answer is beginning to emerge, thanks to an authoritative new study led by Robert Tait at the Australian National University. The scientists looked at the long-term cognitive effects of marijuana use in nearly 2,000 subjects between the ages of 20 and 24. The subjects were divided (based on self-reports) into several different categories, from total abstainers (n = 420) to “current light users” (n = 71) to “former heavy users” (n = 60). Over the course of eight years, the scientists gave the subjects a battery of standard cognitive tests, most of which focused on working memory, verbal memory and intelligence. One of the important advantages of this study is that the scientists controlled for a number of relevant variables, such as education and gender. In Time, Maia Szalavitz explains why this statistical adjustment is necessary:

The lower education levels of the pot smokers — and their greater likelihood of being male — had made it look like marijuana had significantly affected their intelligence. In fact, men simply tend to do worse than women on tests of verbal intelligence, while women generally underperform on math tests. The relative weighting of the tests made the impact of pot look worse than it was.

Once these population differences were corrected for, the long-term effects of marijuana use disappeared: The scientists found that “there were no significant between group differences.” In other words, the amount of pot consumed had no measurable impact on cognitive performance. The sole exception was performance on a test of short-term verbal memory, in which “current heavy users” performed slightly worse than former users. The researchers conclude that, contrary to earlier findings, the mind altering properties of marijuana are ephemeral and fleeting:

The adverse impacts of cannabis use on cognitive functions either appear to be related to pre-existing factors or are reversible in this community cohort even after potentially extended periods of use. These findings may be useful in motivating individuals to lower cannabis use, even after an extensive history of heavy intake.

This study builds on previous work by Harvard researchers demonstrating that the learning and memory impairments of heavy marijuana users typically vanish within 28 days of “smoking cessation.” (The slight impairments still existed, however, one week after smoking.) While several days might sound like a long hippocampal hangover, heavy alcohol users typically experience deficits that persist for several months, if not years. In other words, heavy marijuana use appears to be a lot less damaging than alcoholism.

Taken together, these studies demonstrate that popular stereotypes of marijuana users are unfair and untrue. While it’s definitely not a good idea to perform a cognitively demanding task (such as driving!) while stoned, smoking a joint probably also won’t lead to any measurable long-term deficits. The Dude, in other words, wasn’t dumb because he inhaled. He was dumb because he was The Dude. (All those White Russians probably didn’t help, either.)

Furthermore, there’s some intriguing evidence that marijuana can actually improve performance on some mental tests. A recent paper by scientists at University College, London looked at a phenomenon called semantic priming. This occurs when the activation of one word allows us to react more quickly to related words. For instance, the word “dog” might lead to decreased reaction times for “cat,” “pet” and “Lassie,” but won’t alter how quickly we react to “chair.”

Interestingly, the scientists found that marijuana seems to induce a state of hyper-priming, in which the reach of semantic priming extends to distantly related concepts. As a result, we hear “dog” and think of nouns that, in more sober circumstances, would seem rather disconnected, such as “leash” or “hair.” This state of hyper-priming helps explain why cannabis has been so often used as a creative fuel, as it seems to make the brain better at detecting those remote associations that lead to radically new ideas.

Why does marijuana increase access to far reaching intellectual connections? One possibility is that the beneficial effect of the drug is mediated by mood. Marijuana, after all, has long been used to quiet anxious nerves — big pharma is currently exploring targeted versions of THC as a next generation anxiolytic — as only a few puffs seem to dramatically increase feelings of relaxation and euphoria. (The technical term for this, of course, is getting stoned.) Furthermore, recent research has suggested that performance on various tests of remote associations and divergent thinking — a hallmark of creativity — are dramatically enhanced by such positive moods. Look, for instance, at a 2003 study by German researchers that investigated performance on a classic remote associate test (RAT), in which subjects have to find a fourth word that is associated with the three following words:

cottage Swiss cake

This answer is pretty obvious: cheese. But what about this problem?

dream ball book

That was a trick question: There is no shared association. Here’s the remarkable thing about these remote associate problems: People can recognize the possibility of a solution before they’ve solved the problem. The German scientists demonstrated this by asking people to quickly press the spacebar whenever they were presented with a triad that had an answer. If people had no intuitions about creative associations, their guesses should have been roughly random. But that’s not what the scientists found. Instead, subjects were able to efficiently sort “coherent” word problems — those with an actual answer — from incoherent problems, which are a waste of time. Before we find the solution, we can feel its presence.

And this returns us to marijuana: Putting people in a positive mood roughly doubled their accuracy at the task. All of a sudden, they were twice as good at identifying problems with possible solutions. This suggests that anything that makes us happier, reducing vigilance and anxiety, might also make us more creative. We can detect more remote associations, of course, but we also know which associations are worth pursuing, which is probably even more important. It doesn’t matter if it’s pot, chocolate or a stand-up comic — those substances or experiences that put a smile on our face can also increase the powers of the imagination, at least when solving particular creative problems.

So here’s the very un-D.A.R.E. takeaway: Heavy marijuana use doesn’t seem to cause any sort of lasting brain damage. All the negative side-effects are relatively temporary. (But those side-effects are real.) Furthermore, the sort of anxiolytic giddiness triggered by THC comes with its own unexpected benefits, which is probably why humans have been self-medicating with cannabis for thousands of years.

6 thoughts on “Cannabis and the brain

  1. I suppose that prescription drugs are safe? I am just now going thru a bad period with a prescription reaction. Seeing what chemotherapy does to the human body, causes more problems after you take it then you had before and doesn’t kill the Cancer anyway. I have personally lost too many friends and relatives to Cancer and the current treatments from the medical profession just don’t work. I just wish we had more medical guidance while we take the marijuana and that the Medical community would do the studies that enable us to do so. So far, people on their own, have successfully terminated their own cancers and have suffered no ill effects.


    • She says “products that kill” should be illegal….chemo kills! I just told a troll exactly why it is wrong to say that chemo isn’t poison “like it was in the past”…I saw it being made, if they don’t want a drop of it coming into contact with the skin then it’s obviously not a good idea to inject it. Massive study after study shows that chemo is less than 10% effective at actually saving lives. Many “breakthrough” cancer drugs turn out to be a waste of time or even more harm than good. Working with chemo has been shown to raise the risk of cancer. Then there is the 2012 study on chemo and the WNT16B protein. Then there is the case study of that teenage girl who went into remission solely because of cannabis oil, but died because of damage caused by the chemo.


      • 10% is better than the 0% chance of survival you have if you dont do anything. Chemo works by killing rapid replicating cells in the body, these cells include cancer cells, hair follicles hence the reason why you lose your hair.


  2. Carrie Wofford don’t have a clue what she is on about with no research or facts, people like her make me sick, every recognised educated rich person ie richard branson, albert einstein,Stephen Hawking, and on and on have or do smoke cannabis out of the top 50 world influential people and top brains 39 have or do smoke cannabis, so Carrie Wofford is just making up rubbish with no facts,


  3. I got a recorded 5.5 brain injury on 08-30-2008 when I wrecked my H/D with no helmet on. It killed me 3 times and I was in a coma 87 days. I returned home 14 months later with no memory of what I use to do. They tested me & said I had lost the last 10 years of memory. I had to relearn life again. I had a friend ask me to get a medical card & try “cannabis”. I was amazed, my memories started returning. Since then I have learned that it is THC that does this. Every “head rush” makes the heart pump harder while the THC constricts blood vessels, making the ends of the blood veins grow in thew brain. That is what it needs !


  4. You would have to be mentally retarded to think cannabis kills brain cells or shrinks the brain When the United states governments own resurch says it heals brain cells. Alochol and tobacco use does kill brain cells on the other hand and you know that doctor at least uses one of those. Lmfao ppl these days” I don’t care what The scientific facts are, I’ve been believing a lie my whole life so that makes that lie true!”


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s